Abstract: The performance parameters of a hypersonic inlet (the designed mach number is 6) are computed using finite volume method with three dimensional unsteady compressible N-S equations, and the performance is found descending clearly. In order to improve the inlet performance, laser energy whose power is 15 kW is injected into the flow field in front of the solid cowl of inlet, and then the virtual cowl is formed. The inflow mass capture ratio increases by 34%, 20.6% and 15.6% when the inflow mach number is 4.5, 5 and 5.5 respectively. Pressure contours of the inlet at peak value of inflow mass capture ratio under different mach numbers are illustrated. Characteristics and forming mechanism of the virtual cowl are explained. The results indicate that the smaller the inflow mach number is, the lower the inflow mass capture ratio is, but relative to that without laser energy being injected, the inflow mass capture advancing level is more obvious. Under different inflow mach numbers, the optimum can be achieved through changing the configuration and position of laser induced shock wave. The optimum is the state that transmission wave formed by laser induced shock intersecting with the oblique shock in the leading edge of inflow injects on the inlet shoulder.