The improvement of the emulsifying properties of SPI by papain was researched in this study.The improving degree was studied by single factor experiment and orthogonal experiment with emulsifying activity and emulsion stability as the evaluation index.Results showed that substrate concentration 6%,papain concentration 0.15% and reaction time 0.5 h were the best hydrolysis condition.Under these conditions emulsifying activity and emulsion stability of SPI were increased by 20% and 18%.Substrate concentration was the most important factor,followed by papain concentration,and reaction time with minimal impact.