The flow field characteristics, particle trajectory and liquid film flow characteristics in the supersonic separator were studied by numerical simulation, and the effects of cyclonic flow intensity and droplet diameter on the separation efficiency and liquid film flow rate were analyzed. The results showed that increasing the cyclonic strength or droplet diameter could improve the separation efficiency and liquid film flow rate. The separation efficiency of droplets below 0.1 μm does not exceed 30% when the cyclonic intensity is 0.51. For droplets with diameters not larger than 0.1 μm, the maximum separation efficiency was only 60.90%.