The invention relates to the technical field of microorganism fermentation, in particular to a microorganism fermenting tank for producing a liquid feed additive. The structure of the microorganism fermenting tank for producing a liquid feed additive comprises a fermenting tank body, a heating pipe, a steel sleeve, an outer insulation layer, an electric motor, a sterile shaft seal, a bubble cleaner, a stirring shaft, a stirring machine, an air jetting device, an air filter, a water valve, a sight glass, a digital display thermometer, a feeding opening, a pressure gauge, a PH meter, a dissolvedoxygen detector, an automatic control valve, an exhaust pipe, a sampling pipe, a temperature sensor, a cooling water inlet pipe, a cooling water outlet pipe, a discharging pipe, an air inlet pipe, adischarging pipe valve and a control switch valve. Through the adoption of the microorganism fermenting tank for producing a liquid feed additive disclosed by the invention, the mixing uniformity of fermentation bacteria and a fermentation substrate is improved, quick culture of aerobic bacteria is realized, and the fermenting effect is good; and the microorganism fermenting tank is safe, hygienicand convenient to operate, can be accurately adjusted and controlled, is easy to automate, can be completely used in occasions requiring a fermentation tank which is large in processing capacity andlarge in size, and can provide favorable material bases for popularization and application of microorganism feed additives.