A liquid cooling system for a battery pack, comprising: a liquid cooling plate, a support plate and a water inlet and outlet joint, wherein the liquid cooling plate is provided with a water inlet port, a water outlet port and a liquid flow channel, the liquid flow channel is connected with the water inlet port and the water outlet port, and the water inlet port and the water outlet port are both arranged outside a casing body of the battery pack; the support plate comprises a first through hole and a second through hole, and the support plate is used for fixedly connecting with an outer wall of the casing body of the battery pack and used for sealing and fixing the water inlet and outlet joint; the water inlet and outlet joint comprises a water inlet joint and a water outlet joint, one end of the water inlet joint used for connecting with the water inlet port passes through the first through hole and is connected with the water inlet port in a sealed manner, one end of the water outlet joint used for connecting with the water outlet port passes through the second through hole and is connected with the water outlet port in the sealed manner, wherein the liquid cooling plate further comprises a water inlet connection pipe connected with the water inlet port in the sealed manner, and a water outlet connection pipe connected with the water outlet port in the sealed manner; the water inlet connection pipe is provided with a first inner cavity communicating with the water inlet port, and the water outlet connection pipe is provided with a second inner cavity communicating with the water outlet port, the water inlet joint is provided in the first inner cavity and is connected to a lateral wall of the first inner cavity in the sealed manner, the water outlet joint is arranged in the second inner cavity and is connected with a lateral wall of the second inner cavity in the sealed manner. the liquid cooling plate is provided with a water inlet port, a water outlet port and a liquid flow channel, the liquid flow channel is connected with the water inlet port and the water outlet port, and the water inlet port and the water outlet port are both arranged outside a casing body of the battery pack; the support plate comprises a first through hole and a second through hole, and the support plate is used for fixedly connecting with an outer wall of the casing body of the battery pack and used for sealing and fixing the water inlet and outlet joint; the water inlet and outlet joint comprises a water inlet joint and a water outlet joint, one end of the water inlet joint used for connecting with the water inlet port passes through the first through hole and is connected with the water inlet port in a sealed manner, one end of the water outlet joint used for connecting with the water outlet port passes through the second through hole and is connected with the water outlet port in the sealed manner, wherein the liquid cooling plate further comprises a water inlet connection pipe connected with the water inlet port in the sealed manner, and a water outlet connection pipe connected with the water outlet port in the sealed manner; the water inlet connection pipe is provided with a first inner cavity communicating with the water inlet port, and the water outlet connection pipe is provided with a second inner cavity communicating with the water outlet port, the water inlet joint is provided in the first inner cavity and is connected to a lateral wall of the first inner cavity in the sealed manner, the water outlet joint is arranged in the second inner cavity and is connected with a lateral wall of the second inner cavity in the sealed manner.