Abstract: To study the characteristics of SteamJet engine,the mathematical models of water injection pre-cooling heat-exchange computation,corrected computation of physical property and the engine components characteristics were built.With the models mentioned above,the computation model of SteamJet on basis of the two-spool mix-exhausted turbofan engine with afterburner was built,and the corresponding program was developed.The engine characteristic with different fan inlet total temperatures along flight-trace was computed and the effect of pre-cooling on the afterburner outlet total temperature was analyzed,thus the reasonable fan inlet total temperature was selected,and the altitude and velocity characteristics of SteamJet with afterburner were calculated and analyzed.It's shown from the computation results that,the operating range of turbojet can be expanded greatly with introduction of water injection and pre-cooled method.And compared with the SteamJet without afterburner,the SteamJet with afterburner has better thrust characteristics and can meet the need of hypersonic flight.