Hypersonic turbo/ramjet combined cycle engine concept with the t andem layout was investigated to ensure that the civic aircraft can work reliabl y under a wide range of flight envelope(��Ma��0~5,H=��0~30��km).A non-linear combin e cycle engine model controlled by multiple variables was developed and verified . Based on it, an optimized scheme was then worked out after comprehensive evalu ation on the propulsion system integration via the parametric cycle analysis and performance cycle analysis. This scheme is favorable to the reduction in system dimension and weight, the adjustment of the shared inlet and exhaust nozzle, as well as the stability of the ram combustion. Transient simulation on the turbo/ ram mode transition was also conducted. Results show that stable mode transition could be acquired through proper modulation of five variable geometries and the fuel flow.