Abstract: In order to find out the effect of hydraulic cavitation on the viscosity and molecular weight distribution of pectin, the cavitation effect was generated by the cavitation device and acted on the pectin solution. The change of pectin viscosity before and after hydrodynamic cavitation treatment was studied under different p H, temperature, inlet pressure, initial concentration and reaction time. The effect of hydrodynamic cavitation on pectin was evaluated by the decreasing rate of viscosity. The molecular weight distribution of pectin before and after treatment was analyzed by gel permeation chromatography ( GPC) . The results showed that when the p H of the solution was 5, the temperature was 50 ℃, the pressure of the population was 0.1 MPa, the concentration of pectin was 1 g/L and the treating time was 60 min, the viscosity of the pectin decreased by 15.76%. The GPC analysis showed that the relative average molecular weight of pectin decreased from 70515 to 57408.So the pectin treated by hydraulic cavitation can effectively reduce the viscosity of pectin and its molecular weight, which provided a new method for pectin degradation.