Ultrasound-phosphorylation was used to modify soybean proteins to improve the emulsification property. Based on the single factor experiments, technology was established and optimized by central composite design theory of Box-Behnken. The response model was valid in analyzing and predicting the extent of EAI due to its higher fitting degree and less experimental error. The effect on emulsifying properties of soybean proteins modified by ultrasound-chemistry phosphorylation (UP—SP) were analyzed, and the optimized conditions of preparation of UP—SP were as follows: STP 9.65%, ultrasound power 490 W,and time of reaction 34 min, then the emulsifying activity and emulsion stability of UP—SP, were 70.8 and 30.2min, 2.18 and 1.57 fold against control experiment respectively. The results show that ultrasound-phosphorylation is an efficient method to improve the emulsification properties of soybean proteins.