Soybean protein isolate（SPI）was prepared from defatted soybean meal by alkali extraction and acid precipitation. The optimum condition was obtained by orthogonal experiment,and the alkali solution temperature was 50 ℃, alkali-soluble pH 8, acid precipitation pH 4.0. Soya peptone was prepared from SPI and the preparation techniques were optimized. The result showed that the optimal technical conditions were as follows: reaction temperature 55 ℃, pH value 7.5, substrate concentration 5% and E/S 16 g/kg. All physical and chemical indexes of the obtained soya peptone were similar to the purchased standards. The soya peptone was abundant in essential amino acids with complete varieties and was suitable for culture medium in the preparation of microorganism.