Abstract: Through the combination of wind-tunnel tests and numerical simulations, the shock-wave/boundary-layer interaction (SWBLI) of interstage flow fields within typical stage clearances of a Two-Stage-To-Orbit (TSTO) scaled model at Mach number 6 is studied. Flow fields in the interference areas are analyzed in detail. Results show that the impingement of shock waves induces the boundary layers to transit rapidly to turbulent states, which numerical simulations have accurately captured. SWBLI induces complex three-dimensional flow characteristics with prominent open features. The high wall pressure induced by the strong shock wave spreads downstream in an arc. The incident shock wave generated by the orbiter head constantly reflects between the two stages and gradually weakens. Meanwhile, the spanwise curved principal separation and reattachment lines, streamwise aligned secondary separation and reattachment lines, and critical points, including saddle, node, focus, and vortical structure induced by shear layers, are also observed in the interference areas. The shock wave impingement induces a larger separation area and more obvious open features in the laminar state than in the turbulent state.