Abstract: The characters of fluorescence spectra of soy protein isolate(SPI) solution in vitro of different heat treatment temperature and different heat treatment time. The results showed that heat treatment had a certain effect on the digestion of soybean protein at different heat treatment temperature and different heat treatment time. The best heat treatment condition of soybean protein was 85 ℃,20 min,which was the best degree and effectiveness of the vitro digestion. The soy protein isolate was heat-treated at different temperatures,digested1 h. With the rise of heating temperature,digested products of λ_max increasing redshift,then it started to decrease when the maximum value was reached at 90 ℃.And the fluorescence intensity increased with the heating time,and showed a trend of decline after the first rise. The in vitro simulated digestion of soybean protein isolate 1 h at different heating time,the isolated soy protein digested products of λ_max experienced a process,which was first increased,then decreased. And the fluorescence intensity with the increase of heating time and showed different trends.Growing within 0~20 min,reaching maximum at 20 min,continuing to heat up to 60 min,the fluorescence intensity decreased.