What is claimed is:1. A shielding cover, comprising:a shielding cover body, wherein the shielding cover body comprises a shielding cover body bottom, a first shielding cover sidewall, a second shielding cover sidewall, a third shielding cover sidewall and a fourth shielding cover sidewall, and the first shielding cover sidewall, the second shielding cover sidewall, the third shielding cover sidewall and the fourth shielding cover sidewall are perpendicular to the shielding cover body bottom, respectively; anda shielding cover accessory, wherein the shielding cover accessory is fixedly connected to the shielding cover body, and the shielding cover accessory comprises:an accessory bottom comprising a flat bottom;a connecting arm, wherein the shielding cover accessory is connected to the first shielding cover sidewall of the shielding cover body through the connecting arm; anda positioning arm, wherein the connecting arm and the positioning arm are connected to two opposite ends of the accessory bottom, and the connecting arm and the positioning arm are configured to protrude in opposite directions from the accessory bottom,wherein the shielding cover accessory further comprises a plurality of card slots, the plurality of card slots are arranged at positions of the flat bottom close to the positioning arm, each card slot is configured to penetrate the flat bottom in a direction perpendicular to the flat bottom, and the plurality of card slots are arranged at intervals in a direction parallel to an extending direction of the positioning arm; andwherein the accessory bottom and the positioning arm are located on a side of the connecting arm away from the shielding cover body.2. The shielding cover according to claim 1, wherein a shape of an orthographic projection of each card slot on the flat bottom has a rectangular shape, each card slot has a first size in a direction parallel to the extending direction of the positioning arm and a second size in a direction perpendicular to the extending direction of the positioning arm, and the first size is greater than the second size.3. The shielding cover according to claim 2, wherein the shielding cover accessory further comprises a plurality of first openings arranged on the flat bottom, each first opening is configured to penetrate the flat bottom in the direction perpendicular to the flat bottom, and the plurality of first openings are arranged at intervals in the direction parallel to the extending direction of the positioning arm.4. The shielding cover according to claim 3, wherein the plurality of first openings are respectively arranged adjacent to the plurality of card slots, and a spacing distance among the plurality of first openings in the direction parallel to the extending direction of the positioning arm is greater than a spacing distance among the plurality of card slots in the direction parallel to the extending direction of the positioning arm.5. The shielding cover according to claim 4, wherein the shielding cover accessory further comprises a plurality of first limiting portions, each first limiting portion and the connecting arm are configured to protrude in a same direction relative to the flat bottom, and the plurality of first limiting portions are respectively arranged at the plurality of first openings.6. The shielding cover according to claim 5, wherein each first limiting portion comprises a first limiting sidewall and a first limiting bottom wall, the first limiting sidewall is perpendicular to the flat bottom, and the first limiting bottom wall is parallel to the flat bottom;the first opening has a first opening sidewall away from the card slot adjacent to the first opening, and the first limiting sidewall is connected to the first opening sidewall; andthe first limiting bottom wall is connected to the first limiting sidewall, and the first limiting bottom wall is configured to extend toward the card slot adjacent to the first limiting bottom wall.7. The shielding cover according to claim 6, wherein the accessory bottom further comprises a plurality of recesses, the plurality of recesses and the connecting arm are configured to protrude in a same direction relative to the flat bottom, and the plurality of recesses are arranged at intervals in the direction parallel to the extending direction of the positioning arm; the shielding cover accessory further comprises a plurality of second openings, and the plurality of second openings are respectively arranged in the plurality of recesses.8. The shielding cover according to claim 7, wherein the shielding cover accessory further comprises a plurality of second limiting portions, the plurality of second limiting portions and the plurality of first limiting portions are configured to protrude in the same direction relative to the flat bottom, and the plurality of second limiting portions are respectively arranged at the plurality of second openings.9. The shielding cover according to claim 8, wherein each second limiting portion comprises a second limiting sidewall and a second limiting bottom wall, the second limiting sidewall is perpendicular to the flat bottom, and the second limiting bottom wall is parallel to the flat bottom;the second opening has a second opening sidewall close to a center of the shielding cover accessory, and the second limiting sidewall is connected to the second opening sidewall; andthe second limiting bottom wall is connected to the second limiting sidewall, and the second limiting bottom wall is configured to extend toward the center of the shielding cover accessory.10. The shielding cover according to claim 1, wherein the shielding cover accessory comprises a plurality of first connecting holes, the plurality of first connecting holes are arranged on the connecting arm, and the plurality of first connecting holes are arranged at intervals in the direction parallel to the extending direction of the connecting arm.11. The shielding cover according to claim 10, wherein the shielding cover accessory further comprises a plurality of limiting holes, the plurality of limiting holes are arranged on the connecting arm, and each limiting hole is located between two adjacent first connecting holes.12. A display device, comprising:the shielding cover according to claim 1; anda rear cover connected to the shielding cover.13. The display device according to claim 12, wherein the rear cover comprises a plurality of hook structures, and the plurality of hook structures are respectively matched with the plurality of card slots of the shielding cover.14. The display device of claim 13, wherein the rear cover comprises:a first concave portion configured to receive the shielding cover body;a second concave portion configured to receive the shielding cover accessory; anda positioning bottom and a connecting sidewall arranged in the second concave portion;wherein the first concave portion has a first concave bottom and four concave sidewalls, the second concave portion has a second concave bottom, a first concave sidewall, a second concave sidewall, a third concave sidewall and a concave opening, the first concave sidewall is opposite to the concave opening, the second concave sidewall is opposite to the third concave sidewall, and the first concave portion is communicated with the second concave portion through the concave opening; andthe positioning bottom has a flat surface, a side of the positioning bottom is connected to the second concave bottom through the connecting sidewall, and the other side of the positioning bottom is connected to the first concave sidewall.15. The display device according to claim 14, wherein each hook structure comprises:a body portion, wherein the body portion is configured to protrude toward the shielding cover relative to the positioning bottom; anda hook portion, wherein an end of the hook portion is connected to the body portion, and the hook portion is configured to protrude in a direction toward the first concave sidewall relative to the body portion.16. The display device according to claim 15, wherein the hook portion is spaced from the positioning bottom by a first distance in a direction perpendicular to the positioning bottom, and the first distance is greater than a thickness of the flat bottom of the shielding cover in a direction perpendicular to the positioning bottom.17. The display device according to claim 15, wherein the hook portion has a chamfered portion, the chamfered portion is arranged at an edge of the hook portion facing the first concave sidewall and the positioning bottom, each hook structure further comprises a reinforcing rib arranged on a side of the body portion away from the hook portion.18. The display device according to claim 17, wherein an area of an orthographic projection of each hook structure on the positioning bottom is smaller than an area of an orthographic projection of each card slot on the positioning bottom.19. The display device according to claim 15, wherein the flat bottom of the shielding cover accessory is abutted against the positioning bottom of the rear cover;wherein the accessory bottom of the shielding cover accessory further comprises a plurality of recesses, the plurality of recesses and the connecting arm are configured to protrude in the same direction relative to the flat bottom, and the plurality of recesses are arranged at intervals in the direction parallel to the extending direction of the positioning arm; and the rear cover further comprises a plurality of receiving portions, the plurality of receiving portions are respectively located on two sides of the positioning bottom, and the plurality of receiving portions are configured to respectively receive the plurality of recesses of the shielding cover accessory;wherein the rear cover further comprises a first set of supporting ribs located between the second concave sidewall and one of the receiving portions, and a second set of supporting ribs located between the third concave sidewall and another one of the receiving portions, and each of the first set of supporting ribs and the second set of supporting ribs comprises a plurality of supporting ribs;wherein the display device further comprises a base comprising a bracket, and a part of the bracket is positioned between the shielding cover accessory and the rear cover.20. The display device according to claim 19, wherein the shielding cover accessory comprises a plurality of first limiting portions and a plurality of second limiting portions, and each of the plurality of first limit portions and the plurality of second limit portions comprises a limiting sidewall and a limiting bottom wall,a part of the bracket is positioned between the positioning bottom of the rear cover and the limiting bottom wall, so as to limit a movement of the bracket in the direction perpendicular to the positioning bottom, anda part of the bracket is further positioned between the limiting sidewalls of the plurality of first limiting portions and between the limiting sidewalls of the plurality of second limiting portions, so as to limit a movement of the bracket in a direction perpendicular to the limiting sidewall.