By means of computer simulation for the flow field, the condition of swirling cavitation formation and the shape of cavitation distribution were analyzed with CFD software. The accuracy of simulation results and the validity of wastewater treatment device were verified according to the testing results of device’s working parameters and degradation for Rhodamine B. The criterion to judge cavitation formation or degradation efficiency has been established. The industrialized enlargement for mini wastewater treatment device has been analyzed by means of simulation. It is useful to establish industrial application foundation of this kind of wastewater treatment device.