In order to seek a sidewall compression method to weaken the interaction between swept shock waves of the same side and boundary layers, the three-dimensional flatplate boundary layer generated by the interaction of two swept shock waves of the same side and the flat-plate boundary layer was numerically studied. The flow mechanism of this three-dimensional boundary layer was analyzed. Also, the three-dimensional boundary layer was quantitatively compared with the one generated by one swept shock wave which has the same flow deflection angle. The results show that, in the case of two swept shock waves, the first swept shock wave makes the boundary layer next to the sidewall thinner, so the interaction between the second shock wave and the boundary layer in the attachment region becomes weaker, leading to the total effect that the interaction between two shock waves and the boundary layer is weaker than that at the one swept shock wave case; the total flow deflection angle of two swept shock waves is the same as one shock wave case, so the strength of the converged shock wave is essentially the same; the three-dimensional boundary layer generated by the swept shock is still conical, and the angle between the separation line and the inflow is essentially the same with the one swept shock case.