A design scheme of variable geometry over/under type inlet for turbine-based combined cycle engine was presented.Numerical simulation was carried out to investigate the variation of aerodynamic performance of this variable geometry inlet scheme along flight envelop.On basis of this

the design parameters and geometry modulating law were studied.A superior operating law was acquired.The inlet performance of typical work point was provided.Results indicate that the total pressure recovery coefficients at throat section of turbine inlet and exit section of scramjet inlet are not less than 0.69 and 0.38 under different freestream Mach number.