Abstract: The effects of pectin concentration, dry-heat temperature and dry-heat time on the molecular structure of sweet potato starch were studied by electron microscopy, ultraviolet-visible spectroscopy and particle size analyzer.The results showed that the granules blended with starch and pectin formed a small clump with the extension of time, and became bigger after heat treatment at different time.The degree of polymerization between starch and pectin was decreased with the increase of pectin concentration ( from 620 ~ 626 nm without adding to 603 ~ 608 nm with pectin concentration of 0.05%) , and the degree of polymerization between starch chains weakened with the increase of temperature and time, the maximum absorption wavelength of UV spectrum showed a blue shift.The particle size ( D50) and the volume fraction of big starch particles of starch granules increased with the increase of pectin concentration, temperature and time. The particle size ( D50) of starch granules was the largest at dry-heat time of 3 h ( 15.47 μm) , and the volume fraction of big starch particles could reach 6.27%, which was1.81% higher than that at 1 h. The declined leakage of amylose was better inhibited by the increase of pectin concentration ( 0.01% ⁰.04%) , dry-heat temperature and time ( 1⁴ h) .Dry-heat treatment is a new method of physical modification of starch, which is of great significance to improve sweet potato starch utilization rate and develop new type modified starch.