Abstract: Shock wave boundary layer interaction in compressor cascades is an extremely complicated problem. In case of the existance of the separation, it is one of the most important factors which determine the performances of transonic compressor.However, no thorough investigation has been made on shock wave boundary layer interaction in compressor cascades and only a few papers on this topic have been published.It is shown by calculation and analysis that the main form of the interaction in compressor cascades is the interaction between shock wave and turbulent boundary layer in channels.The analysis has made clear that the separation criterion proposed by Pearcey is an empirical criterion obtained from wind tunnel tests of a RAE102 airfoil. The conditions are quite different from the restrained channel flow in compressor cascades with strong adverse pressure gradient. As for compressor cascades, the boundary layer grows rapidly and separates at lower Mach number upstream of the shock wave, the length of separated region and the location of vortex sheet are all different from those in the case of Pearcey's single airfoil. The conclusion has been drawn that it is inappropriate to apply Pearcey's separation criterion directly to shock wave boundary layer interaction in compressor cascades.It is proposed that the separation criterion for shock wave boundary layer interaction in compressor cascades be in the form f （M1, p1/p1.E., pT.E./p2,Rec） = 0 , which involves the effects of pressure gradients in front of and behind the shock wave.