The invention discloses a quick dismounting and replacement device for a middle battery box in an electric vehicle (EV). The structure comprises a lifting and lowering rod, a lifting-and-lowering-typebattery box displacement layer, a dismounting and replacement device body, a battery box quick dismounting and replacement passage, a cross rod, side plates, a movable valve, a fixed base and a pullhandle. Through the connection between a lifting and lowering support frame and a battery box storage layer, a battery box replacement displacement layer and a used battery box placement layer, the quick dismounting and replacement device for the middle battery box in the EV can lift, lower or expand each layer in an orderly manner as needed when dismounting and replacing batteries. A scale bar isarranged to accurately adjust the lifting and lowering height so as to meet the replacement space requirements of different vehicles. In addition, through the cooperation between the lifting-and-lowering-type battery box displacement layer and the battery box quick dismounting and replacement passage, calibration adjustment sliding frames can adjust and fix the conveying position of the battery box during the alternation and replacement of the batteries, so as to prevent the occurrence of deviation and to ensure the accuracy of the replacement of the battery box to a middle layer of the EV. The connection between a driving device and a conveying track can assist the conveying process and increase the dismounting and replacement speed.