In this paper, the effects of ultrasonic on the degradation kinetics, structure properties, and antioxidant activity of hawthorn pectin were studied. According to our study, as ultrasonic time extended, the intrinsic viscosity for different hawthorn pectin concentrations decreased. The ultrasonic degradation of hawthorn pectin reaction conformed to the first-order kinetic equation. As the reaction rate constant (k) decreased, hawthorn pectin concentration increased. When ultrasonic time was 10 min, the Gal A increased by 10.62% and the DE decreased by 45.57% compared with control, additionally, the particle size, turbidity and gel properties of hawthorn pectin decreased. Hawthorn pectin molecular weight and its distribution all decreased after ultrasonic treatment. FTIR analysis indicated that ultrasonic treatment did not change pectin's primary structures, and SEM analysis showed that the surface characteristic of ultrasonic treatment pectin was different from native pectin. Moreover, in vitro antioxidant activity assays indicated that ultrasonic treatment significantly improved the antioxidant activity of pectin. It was concluded that ultrasonic treatment not only affected the properties of pectin, but also affected its antioxidant activity.