A battery module for an electric vehicle, the battery module comprising: an external case fixed in the electric vehicle, and comprising an accommodation space and a first fixing part; a battery box detachably installed in the accommodation space; a fixing mechanism disposed on the battery box, wherein when the battery box is installed in the accommodation space, the fixing mechanism is engaged with or disengaged from the first fixing part, so that the battery box is selectively in a locked status or an unlocked status, wherein when the battery box is in the locked status, the battery box is securely fixed in the accommodation space, wherein when the battery box is in the unlocked status, the battery box is removable from the accommodation space; and a rotatable pull tab, wherein by rotating the rotatable pull tab, a relationship between the fixing mechanism and the first fixing part is adjustable, so that the battery box is selectively in the locked status or the unlocked status, wherein when the battery box is in the unlocked status, the battery box is removed from the accommodation space in response to an external force exerted on the rotatable pull tab; wherein the fixing mechanism further comprises a second fixing part corresponding to the first fixing part, wherein the second fixing part is disposed on an outer surface of the battery box, wherein the outer surface of the battery box faces an outer side of the external case, and the second fixing part is engageable with the first fixing part; wherein the first fixing part is an indentation, and the second fixing part is a pin; characterized in that the rotatable pull tab is detachbly inserted into the fixing mechanism and the fixing mechanism further comprises: a rotatory disk rotatably disposed on the outer surface, and connected with the pin through a connecting rod action, wherein upon rotation of the rotatory disk, the pin is rotated relative to the outer surface, so that the pin is partially protruded out of the outer surface or the pin is not protruded out of the outer surface, wherein when the battery box is in the locked status, the pin is engaged with the indentation, wherein when the battery box is in the unlocked status, the pin is disengaged from the indentation; and a guiding disk rotatably covering the rotatory disk for synchronously driving rotation of the rotatory disk, wherein the guiding disk comprises a recess. an external case fixed in the electric vehicle, and comprising an accommodation space and a first fixing part; a battery box detachably installed in the accommodation space; a fixing mechanism disposed on the battery box, wherein when the battery box is installed in the accommodation space, the fixing mechanism is engaged with or disengaged from the first fixing part, so that the battery box is selectively in a locked status or an unlocked status, wherein when the battery box is in the locked status, the battery box is securely fixed in the accommodation space, wherein when the battery box is in the unlocked status, the battery box is removable from the accommodation space; and a rotatable pull tab, wherein by rotating the rotatable pull tab, a relationship between the fixing mechanism and the first fixing part is adjustable, so that the battery box is selectively in the locked status or the unlocked status, wherein when the battery box is in the unlocked status, the battery box is removed from the accommodation space in response to an external force exerted on the rotatable pull tab; wherein the fixing mechanism further comprises a second fixing part corresponding to the first fixing part, wherein the second fixing part is disposed on an outer surface of the battery box, wherein the outer surface of the battery box faces an outer side of the external case, and the second fixing part is engageable with the first fixing part; wherein the first fixing part is an indentation, and the second fixing part is a pin; characterized in that the rotatable pull tab is detachbly inserted into the fixing mechanism and the fixing mechanism further comprises: a rotatory disk rotatably disposed on the outer surface, and connected with the pin through a connecting rod action, wherein upon rotation of the rotatory disk, the pin is rotated relative to the outer surface, so that the pin is partially protruded out of the outer surface or the pin is not protruded out of the outer surface, wherein when the battery box is in the locked status, the pin is engaged with the indentation, wherein when the battery box is in the unlocked status, the pin is disengaged from the indentation; and a guiding disk rotatably covering the rotatory disk for synchronously driving rotation of the rotatory disk, wherein the guiding disk comprises a recess. a rotatory disk rotatably disposed on the outer surface, and connected with the pin through a connecting rod action, wherein upon rotation of the rotatory disk, the pin is rotated relative to the outer surface, so that the pin is partially protruded out of the outer surface or the pin is not protruded out of the outer surface, wherein when the battery box is in the locked status, the pin is engaged with the indentation, wherein when the battery box is in the unlocked status, the pin is disengaged from the indentation; and a guiding disk rotatably covering the rotatory disk for synchronously driving rotation of the rotatory disk, wherein the guiding disk comprises a recess.