The 3-D flow fields in a variable geometry inlet on combined engine at different Mach numbers were numerically analyzed.The characteristics of the inlet flow at different Mach numbers were compared and discussed.The results show that the spillage increases and the mass flow ratio decreases with the decline of the Mach number.The first internal shock and its reflective position are important to organize the flow field in the internal passage.With backpressure at the exit of the inlet

the shock train could be formed in the diffuser.The free stream Mach number

backpressure and flow condition in the internal passage determine the form and position of the shock train.The conclusions may be useful to the research for variable geometry inlet on combined engine.