In order to evaluate the influence of ultrasonic cavitation on mixing, based on the method of UFD (User Defined Function), the flow field in the mixer（KSM）was numerical simulated by using FLUENT software and verified by experiment. The results showed that the fluid in the KSM mixed faster and more uniform due to the ultrasonic cavitation. The pressure drop of the mixer increased slightly. The flow rate of the fluid increased from 0.50 m/s to 0.55 m/s at the inlet of the mixer and it increased by 10%. The turbulence intensity of the fluid was enhanced, and the strengthening effect was most significant at the first mixing element. And more important, the strengthening effect was most significant for the first element which is basically stable after second mixing elements. The result of experiment also is basically consistent with the simulation results. The fluid mixed more uniform and the mixing was better. With the addition of ultrasonic cavitation, the mixing of the fluid in the static mixer was more uniform and the mixing effect was better.