Abstract: In order to study the structure change of food components in the ultrasonic field, the changes of granular appearance and crystallian structure of potato starch after treated by ultrasonic field were investigated with the polarized light microscope and the x-ray diffraction. Results show that the granular appearance of potato starch is destroyed to some extend in the ultrasonic field. The starch granular appeared alveolate shape, and the more ultrasonic time the potato treated the more holes appeared. With the increase of the ultrasonic time, the partial starch granular deformed or vanished evenly. Polarized light cross microphotoes and x-ray diffraction patterns show that the crystallian structure of potato starch does not change, and the non-crystallization areas of potato starch are the main areas affected by the ultrasonic field field.