Abstract: When Reynolds number and the blade surface pressure coefficient distribution are kept constant,the influence of the inlet Mach number on the boundary layer development on the blade surfaces of turbomachinery is discussed with numerical simulation as well as an order of magnitude analysis,based on the integral boundary layer equation.The effects of surface curvature and the free stream turbulence intensity on the development of the boundary layer are also estimated by the numerical simulation.The results show that at the same Reynolds numbers and surface pressure coefficient distributions,the variation of the non dimensional the integral parameters boundary layer with the inlet Mach number is very small,up to the critical Mach number,the changes are usually within the engineering tolerance.The variation caused by the surface curvature difference is of the same order of that due to Mach number,however the free stream turbulence level can cause remarkable changes in the development of the boundary layer.