The present invention discloses a quantity detecting method of microbe, specifically relating to a quantity detecting method for bacillus of microbe fertilizer. The method is characterized in that: disposing a sample to be detected through simple and practical physical method; adsorbing according to the normal method; coating utensil; growing visible bacterial colony on the board after 2-3d; counting and calculating normal bacterial colony; and obtaining the quantity of pure germ in the sample. The detecting method provided by the present invention is suitable for detecting product quality of microbial fertilizer produced by bacillus and other microbial fertilizer product. Moreover, the proportion between germ and trophozoite in the product can be better learned about so that the detection result of the manufactured product can be more conformed to the practical viable count at expiration of the product, thus being good in guiding production and guaranteeing product quality. Comparing with the prior art, the detecting method is more simple, convenient, accurate, and practical.