Design of the thermal protection system (TPS) with the forward-facing cavity and opposing jet combined configuration was investigated numerically for the hypersonic vehicle.The numerical method was validated with the related experiments.The flow field parameters and surface heat flux distribution were obtained by solving the Navier-Stokes (N-S) equations.The validity of the combined TPS was testified and the effect of the cavity physical dimension on cooling efficiency of the combined TPS was discussed.The results show that the TPS with smaller diameter cavity has smaller aerodynamic heating and the TPS with larger length cavity has higher heat flux reduction.The recirculation region plays a pivotal role for the reduction of heat flux.The aerodynamic heating is more sensitive to the changing of the cavity diameter than the cavity length.