Grape seed proanthocyanidins （GSP） were added to potato steamed bread in different proportions. The digestible properties of starch in potato steamed bread were studied by in vitro simulated digestion. Rapid viscosity analysis， X-ray diffraction and Fourier transform infrared spectroscopy were used to explore the mechanism of GSP inhibiting starch digestion properties in potato steamed bread. Results showed that GSP could significantly reduce the content of rapidly digestible starch and increase the content of slowly digestible starch and resistant starch. FTIR and XRD showed that GSP might bind with starch in potato steamed bread by non-covalent forces such as hydrogen bonding. In addition， GSP significantly increased the viscosity of potato steamed bread powder， which may promote the stability of steamed bread's structure. GSP is a potential functional additive that could be used to reduce the digestibility of starch in potato steamed bread.