Abstract: In order to identify the chemical feature of potato starch which contains no protein, the potato starch and potato amylose were hydrolyzed by alkali protease and the change of their chemical structure were analyzed by IR, ESI- MS, 1H and13 C nuclear magnetic resonance spectroscopy. The results showed that hydrolysis of potato starch by protease changed the interaction pattern of potato amylose and amylopectin, which led to the loss of C- H stretching vibration of methelene.Interaction of amylose and protease altered the pattern of water in starch.Protease hydrolysis increased the amorphous phase of potato starch and amylose. Protease hydrolysis of potato starch caused the changes of potato starch in13 C NMR peaks at 69.2, 68.3, 68.0, 66.3, 38.3ppm and1 H NMR peaks around 4.7, 3.6, 3.3ppm. Analysis results of IR and ESI- MS suggested that the Asp, Leu and Glu- C peptides probably joined the connection of protein and potato starch.