In this experiment， five kinds of soy protein isolate as raw materials， using a variety of protein analysis and detection methods， study in structure changes of in vitro digestion process soy protein isolate. Fitting FT-IR and Raman spectroscopy result of soy protein isolate and digestion products showed that the changes of content of the secondary structural elements were basically the same， a negative correlation was found between DH and α-helix， β-sheet content. Tyrosine residues of soybean protein isolate and digestion products tend to be“exposed”. The increasing λmax with digestive time and decreased Raman band intensity of tryptophan suggested that tryptophan residues tend to hydrophilic microenvironment. Five different varieties of soy protein isolate after 5 h of continuous digestion in vitro experiments， the degree of hydrolysis increases with time， but after 1h after digestion， the growth rate of DH slowed down and under the same conditions， DH differences between different samples.