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The study used the functional Lactobacillus acidophilus producing α-amylase, protease, phytases and β-mannanase to carry out cooperative fermentation of soybean meal. The effects of the inoculating amount, fermentation temperature, fermentation time and the ratio of water to material on the content of acid-soluble protein were studied by the single factor experiment. On this basis, through Box-Behnken design experiment, the quadratic regression model was established, and the optimal fermentation conditions were the inoculated amount of bacterial liquid of 12.3%, the fermentation time of 78.9 h, the fermentation temperature of 36.8 °C, and the ratio of water to material of 0.9 L/kg. Under these conditions, the crude protein content increased by 15.13%, the acid-soluble protein content increased by 66.91%, hemicellulose content decreased by 24.93%, the free amino acid content was 11.62 times higher before fermentation, the trypsin inhibitor content decreased by 91.68%, the urease activity decreased by 95.67%, the phytic acid content decreased by 83.87%, and the viable bacteria count in fermented soybean meal was 1.37x1010 CFU/g. The study indicates that the composite strain fermentation mode can effectively improve the nutrient composition of soybean meal and remove antinutrient factors, so as to improve the utilization rate of soybean meal and provide a reference for the industrial production of fermented soybean meal. [ABSTRACT FROM AUTHOR]