Abstract: Low temperature defatted soybean protein was treated by thermal modification in the acid condition, and the influence of different heating temperature, pH and heating time on the emulsification was studied. The best modified conditions was obtained through the orthogonal test:the best heating temperature was 50℃, pH was 6.0, and the heating time was 60min, emulsification of the modified sample was increased by 31.3% , even reached 41.7% , when the concentration of Na + (mass fraction) was 1.0% . And structure of the modified soy protein was verified to have changed by endogenous fluorescence scan at 280nm. It showed that the change of protein structure had an important impact on the emulsification.