Abstract: In the present work, the process of steam-jet ejector was analyzed in detail.Three thermodynamic models for calculating entrainment ratio of steam-jet ejector:the ideal model, the momentum conservation model and the kinetic energy conservation model were deduced according to the change in thermodynamic state.The IAPWS-IF97 formulation was used to compute steam properties,and the effects of nozzle, mixing and diffuser efficiency on ejector performance were studied.Although there was some difference between the MC model and the ideal model when no imperfect factors were considered, however, it was found that the MC model represents the empirical curves better than the KEC model if reasonable efficiencies were used.