A liquid nitrogen tank includes a tank, a storage rack and a drive component. The tank includes a tank cover, a tank body, a vacuum cavity layer and a heat-insulating cavity layer. The tank cover is disposed to cover on the tank body. An access door is provided on the tank body. A storage cavity is provided in the tank body. The heat-insulating cavity layer is provided on a periphery of the storage cavity. The vacuum cavity layer is provided on a periphery of the heat-insulating cavity layer. The storage rack is provided in the storage cavity. A plurality of cryopreservation tube racks are stored in the storage rack. The drive component can drive the storage rack to rotate and move up and down in the storage cavity, and can drive the plurality of cryopreservation tube racks to move to a position corresponding to the access door.