The soybean polypeptides prepared by microbial fermentation of high-temperature soybean meal have characteristic of low production cost and high hydrolysis.Using enzyme activity as index,high-yield proteinase producing strain was screened by UV mutagenesis and genetic stability test in this study.Using hydrolysis degree as surveillance index,the strain was used to ferment extrusion and expansion of high-temperature soybean meal,and the fermentation process was optimized.The conditions of UV mutagenesis were as follows: UV watt was 20,irradiant distance was 35cm,irradiant time was 4min.Optimation of medium was performed by single factor and L_9(3~4) orthogonal experiments.The composition of optimal medium was as follows: soluble starch 2.5%,magnesium sulfate 0.04%,soybean meal 10% and Tween-80 0.5%.The cultural condition determined by single factor experiment was as follows: temperature 30℃ for 44 h,inoculum 4%,culture-age 21 h,agitation 200r/min,medium volume 30 mL/250 mL,initial pH 7.5.Using the described optimum medium and condition,hydrolysis degree of high-temperature soybean meal could reach 22.86% which was 8.34% higher than before.