The Fluent software was used to simulate the twodimensional flow field in a steam ejector, and the effect of working fluid pressure, back pressure and nozzle position on the jet performance was studied, and the development and end of the shock wave in the flow field of the ejector were analyzed. The results show that the working fluid pressure, back pressure, nozzle position of the steam ejector all have corresponding optimal value at certain conditions, and the shock wave generation and end position have a great influence on the performance of the ejector. When the first shock wave is produced by the nozzle exit and extended to the outlet vicinity of the mixing section, the second shock wave is ended at the inlet of the diffusion chamber, the ejection coefficient is the largest.When the shock is ended too early or too late, the performance of the ejector will be affected.