The invention discloses a fermentation method of soybean paste. The method comprises the following steps of: 101) preparing osmophilic active microorganism, hyperosmotic culture medium and soybean paste material; 102) carrying out incline activation to the osmophilic active microorganism with the hyperosmotic culture medium, and then carrying out liquid spread cultivation to obtain a culture solution; 103) mixing the culture solution with brine to obtain mixohaline; 104) adding the mixohaline into the soybean paste material for stirring and fermentation; and 105) after the fermentation is accomplished, obtaining the soybean paste. The soybean paste material can also be mixed in the brine firstly to obtain soy sauce mash for fermentation, the culture solution is added during the fermentation process, and then the fermentation is continued to obtain the soybean paste. The fermentation method of soybean paste not only can achieve the purpose of preventing tyrosine white material from precipitation, but also has the advantages that the operating condition is mild, the method is not influenced by starter propagation conditions, the operation is simple and convenient, the efficiency is high, and simultaneously, the flavor of the soybean paste is not influenced.