The invention relates to a method for producing renninum by liquid state fermentation of red yeast rice, belonging to the technical field of biological engineering and enzyme preparation. The method comprises the following steps: liquid state fermentation of the red yeast rice; precipitation of organic solvent; low temperature centrifugation; vacuum freeze drying; Sephadex G-75 gel column chromatography; and DEAE-cellulose 52 chromatography. By the method, high-activity renninum can be prepared by raw materials with low cost so as to greatly solve the problem of deficient source of the renninum.