The invention provides a liquid fermentation tank which comprises a tank body and a stirring device. The stirring device comprises a ring-shaped hollow guide rail which is fixed to the inner wall of the tank body, a second air inlet pipe which hermetically passes through the tank wall and then is communicated with the guide rail, and a support ring which is coaxially arranged in the guide rail; an opening is formed in the inner side of the guide rail, and a sterilizing filter and a first check valve are arranged on the second air inlet pipe one by one in the air inlet direction; the support ring can rotate about the axis of the support ring, and the inner side of the support ring is in contact with the inner wall on the side, provided with the opening , of the guide rail; a plurality of connecting pipes passing through the opening are uniformly arranged on the inner side of the support ring in the circumferential direction, a mixing blade is arranged at the end, located outside the guide rail, of each connecting pipe which is communicated with the guide rail, and an air jet hole is formed in each connecting pipe. The liquid fermentation tank eliminates the need for a motor, a reducer and a mixer shaft which are required for the traditional mechanical stirring, enables the weight of the whole fermentation tank to be lower, and is low in cost.