Abstract: In order to understand the change of intrinsic viscosity of potato starch in ultrasonic field and its mechanism,the change of intrinsic viscosity of starch was measured by Ubbelohde viscometer. Fourier transform infrared spectroscopy(FT-IR)combined with UV-Vis spectrophotometer was used to characterize the properties of potato starch paste after ultrasonic treatment. The results showed that,the intrinsic viscosity of potato starch paste decreased with the extension of ultrasonic time the increase of ultrasonic intensity;the influence of ultrasonic field on diluted starch paste was greater;the lower the concentration of potato starch paste,the greater the decrease of intrinsic viscosity,and the smaller the intrinsic viscosity of potato starch paste. Fourier transform infrared spectroscopy showed that the structural units α-D-glucosamine that made up the starch molecule did not change significantly in the ultrasound field. After ultrasonic treatment,the amylose content of potato starch paste increased,and the size of bond energy was analyzed. It was deduced that the position of chain scission of potato starch paste in ultrasonic field might occur on the glycosidic bond C-O. Ultrasound caused breakage of the potato starch molecular chains,and the intrinsic viscosity of the potato starch paste was reduced.