A liquid cooling plug-in assembly, a liquid cooling plug-in device, and a battery pack assembly are provided. The liquid cooling plug-in assembly includes a first fixed plate, a floating plate, at least one first elastic member, and a plurality of plug-in members, the plurality of plug-in members are all connected to the floating plate, the first fixed plate is provided with a movement cavity therein, the floating plate and the first elastic member are both located in the movement cavity, and the floating plate is in floating connection with the first fixed plate by means of the first elastic member.