The invention relates to a microbial fermentation tank. The microbial fermentation tank comprises a tank body, the tank body top is provided with a feed inlet, a vent port and an observation window. The tank body is internally provided with a stirring motor, supporting seats are disposed on two sides of the stirring motor, support rods are disposed between the stirring motor and the supporting seats, the supporting seats, the support rods and the stirring motor are connected in order, the lower end of the stirring motor is provided with stirring rod, the lower end of the stirring rod is equipped with a first stirring blade and a second stirring blade, and the bottom end of the tank body is provided with a discharge port. The microbial fermentation tank provided by the invention has the advantages of precise control of in-tank temperature, observation of in-tank fermentation condition at any time, and difficult shaking during stirring.