[Purposes] Vortex tubes are widely applied in various industrial sectors of fixed-point or small-scale refrigeration. However, the low efficiency and small cooling capacity restrict their large-scale application. The energy separation efficiency of a supersonic vortex tube was analyzed to study methods for optimizing the efficiency of vortex tubes. [Methods] A supersonic vortex tube was designed by replacing the convergent nozzle in the traditional vortex tube with a Laval nozzle. The energy separation efficiency of the supersonic vortex tube was investigated under varying structural and operational parameters through numerical simulation and experiments. The working conditions under high inlet pressure were calculated, and experiments were conducted at low pressure. The effects of length-to-diameter ratio, Mach number, and inlet pressure on the energy separation efficiency of the supersonic vortex tube were obtained. [Findings] The variation trends of the efficiency curves of the supersonic vortex tube in the numerical simulation results are roughly the same as those in the experimental results. When the inlet pressure is 12 MPa, the optimal cooling effect of the supersonic vortex tube with the length-to-diameter ratio of 25 can reach 57.01 K. [Conclusions] The cooling and heating effects of the supersonic vortex tube are good, but its optimal cooling efficiency is lower than that of the traditional vortex tube. Within a specific range, increasing the length-to-diameter ratio, Mach number of the nozzle outlet flow, and inlet pressure can enhance the energy separation efficiency of the supersonic vortex tube.