The invention discloses a complex microbial agent for producing soybean paste in Pixian County, which mainly comprises coculture of saccharomyces cerevisiae, candida utilis, lactobacillus plantarum and salt tolerant tetrads, and skim milk powder, glycerin, maltodextrin, trehalose and L-sodium glutamate, or mainly comprises coculture of saccharomyces cerevisiae, candida utilis, lactobacillus plantarum and salt tolerant tetrads, and porous starch, maltodextrin and polyvinyl pyrrolidone. A method for preparing the complex microbial agent for producing soybean paste in Pixian County comprises the following technological steps of: (1) activating and propagating strains; (2) inoculating; (3) co-culturing; and (4) adding a protective agent and drying. By using the complex microbial agent in the preparation of cooked soybean paste, the complex microbial agent maintains the characteristics of traditional soybean paste in Pixian County. Meanwhile, compared with the traditional technology, the complex microbial agent has the advantages of shortening the production period by 1/3, improving the amino nitrogen content by 3 to 8 times, improving the volatile aroma content by 2 to 4 times, and ensuring the aflatoxin B1 of 0 to 0.5ppm only.