Abstract: A type of supersonic separation structure is designed according to natural gas field condition and gas well drilling technology parameters. Based on the new device, a reasonable three-dimensional CFD model is established, and the realizable k-ε turbulence model is selected to simulate the internal flow field of the supersonic separator. The separation parameters such as pressure, temperature, Mach number, and turbulence kinetic energy along the axis inside the supersonic separator are investigated, the flow characteristics along the radial direction in different sections are also discussed. The simulation results show that when the pressure loss ratio is 47. 5%, the shock wave will occur in divergent of the Laval nozzle (about 98 mm from the entrance of the supersonic separator) . Due to the expansion effect of the Laval nozzle, the lowest temperature will achieve 190. 52 K. The calculation result agrees well with the previous experimental result. The new separator structure can also produce strong swirling intensity.Besides the calculation method gives a good guidance for the optimal design of the supersonic separator dimensions.