The in vitro digestion of sweet potato starch and potato starch was simulated to explore the changes of digestion characteristics and structure of sweet potato starch during digestion. The effects of digestion time on the physical and chemical properties and structure of sweet potato starch and potato starch were observed by laser particle size analyzer， rheometer， scanning electron microscope and X-ray diffraction. The results showed that the digestion rate of sweet potato starch was slightly higher than that of potato starch. The amylopectin content of the two kinds of starch decreased during digestion， and there was no significant difference in amylose content. During digestion， starch viscosity decreased with the extension of digestion time. The particle size distribution of digested products showed a multi-peak distribution， and the median particle size shifted radically with the extension of digestion time. The crystallinity of starch increased with the extension of digestion time in the later stage of digestion. The morphological appearance of the two starches changed from smooth surface particles to porous or even small clusters under the action of enzymatic hydrolysis of digestive solution. On the whole， the change trend of sweet potato starch and potato starch in the process of digestion was basically the same.