What is claimed is:1. An air deflection plug-in box for a forced air-cooled cabinet, comprising:a front vertical plate with one or more vent holes,a rear vertical plate with one or more vent holes,two side vertical plates with hangers; andan air deflection diaphragm arranged to isolate air areas,wherein the front vertical plate, the rear vertical plate, the two side vertical plates and the air deflection diaphragm are fixedly connected into a whole to divide the air deflection plug-in box into a first space and a second space, and the first space and the second space are used to guide cold airflow and hot airflow respectively,wherein a thermal barrier is arranged on each of two surfaces, close to the first space and the second space, of the air deflection diaphragm, and each thermal barrier is made from thermal insulation material;wherein one end, connected with the front vertical plate, of the air deflection diaphragm is lower than another end, connected with the rear vertical plate, of the air deflection diaphragm; a thickness of the thermal barrier on each of two surfaces of the air deflection diaphragm gradually increases along a direction from a region near the front vertical plate to a region distant from the front vertical plate.2. The air deflection plug-in box as claimed in claim 1, wherein the thermal barrier is arranged on an inner side surface of a first part, which guides the cold airflow, of each of the two side vertical plates.3. The air deflection plug-in box as claimed in claim 2, wherein one or more vent holes are arranged in a surface of a second part, which guides the hot airflow, of each of the two side vertical plates.4. The air deflection plug-in box as claimed in claim 2, wherein at least one sound absorber is arranged on one or more inner side surfaces of the air deflection plug-in box.5. The air deflection plug-in box as claimed in claim 4, wherein the at least one sound absorber is arranged on a side, close to an external fan, of the air deflection diaphragm.6. A forced air-cooled cabinet, comprising one or more functional plug-in boxes and one or more air-deflection plug-in boxes, wherein each functional plug-in box comprises an air-cooling fan arranged at a top end of the functional plug-in box or a bottom end of the functional plug-in box, the one or more functional plug-in boxes and the one or more air deflection plug-in boxes are alternately stacked, and each air deflection plug-in box is the air deflection plug-in box as claimed in claim 1.7. A forced air-cooled cabinet, comprising one or more functional plug-in boxes and one or more air-deflection plug-in boxes, wherein each functional plug-in box comprises an air-cooling fan arranged at a top end of the functional plug-in box or a bottom end of the functional plug-in box, the one or more functional plug-in boxes and the one or more air deflection plug-in boxes are alternately stacked, and each air deflection plug-in box is the air deflection plug-in box as claimed in claim 2.8. A forced air-cooled cabinet, comprising one or more functional plug-in boxes and one or more air-deflection plug-in boxes, wherein each functional plug-in box comprises an air-cooling fan arranged at a top end of the functional plug-in box or a bottom end of the functional plug-in box, the one or more functional plug-in boxes and the one or more air deflection plug-in boxes are alternately stacked, and each air deflection plug-in box is the air deflection plug-in box as claimed in claim 3.9. A forced air-cooled cabinet, comprising one or more functional plug-in boxes and one or more air-deflection plug-in boxes, wherein each functional plug-in box comprises an air-cooling fan arranged at a top end of the functional plug-in box or a bottom end of the functional plug-in box, the one or more functional plug-in boxes and the one or more air deflection plug-in boxes are alternately stacked, and each air deflection plug-in box is the air deflection plug-in box as claimed in claim 4.10. A forced air-cooled cabinet, comprising one or more functional plug-in boxes and one or more air-deflection plug-in boxes, wherein each functional plug-in box comprises an air-cooling fan arranged at a top end of the functional plug-in box or a bottom end of the functional plug-in box, the one or more functional plug-in boxes and the one or more air deflection plug-in boxes are alternately stacked, and each air deflection plug-in box is the air deflection plug-in box as claimed in claim 5.
