Using separated soybean protein as raw material, Alcalase as proteinase, the effects of substrate concentration, temperature, enzyme concentration, pH and time of enzymatic hydrolysis on hydrolysis degree in soybean protein were studied in this paper. The optimal conditions of hydrolysis were obtained by orthogonal experiment as follows: substrate concentration 3%, pH 8.0, enzyme concentration 5%, temperature 55℃, and the time of enzymatic hydrolysis 6 h. Under these conditions, nice taste and high yield of peptides was obtained.