Turbo-ramjet combined propulsion system for a hypersonic transport was examined, which can work steadily and reliably in a wide flying-scope(��Ma��0~5,H��=0~30?km). The overall performance simulation of turbo engine and ramjet engine was accomplished. The simulation of turbo/ramjet mode transition and the steady performance of the combined cycle engine along the aero track was nearly achieved. The performance simulation model includes variable geometry and variable cycle. The model had been tested by testing data. Based on the models of turbo and ramjet engine for hypersonic flight, the engine with afterburner was analyzed and compared with the one without afterburner. The influence of the flux matching with engine and inlet for the turbo engine on the engine performance was analyzed at the same time. At the end, it is shown that the calculational performance of turbo/ramjet mode transition for an "over-under" concept, turbo-ramjet combined engine.