During the machining of powder metallurgy (PM) superalloy parts, the machined surface undergoes severe plastic deformation which appears to be in the form of microstructure and mechanical properties transformation. White layer which is belong to the microstructure and mechanical properties transformation, usually generated on the machined surface during hard machining of PM superalloy, it has significant effect on the machined surface quality. The effect of cutting speed on the white layer formation has been successfully investigated in order to illustrate the microstructure and mechanical properties transformation in the machined surface of PM superalloy FGH95. White layer thickness on the machined surface increased with the increasing of cutting speed. The investigation results showed that machined surface exhibited densification with no obvious structural features characteristics. FGH95 superalloy bulk material existed in the form of Ni-based solid solution, while the microstructure of white layer was observed significantly different from bulk materials. It’s because of the transformation of microstructure presented in the form of Ni-based solid solution in FGH95 during the cutting process. The higher the cutting speeds more severe grain refinement, which will leads to higher values of hardness in white layer. Residual stresses in the machined surface of FGH95 were seems to be observed tensile in all cutting conditions and it was observed an increasing trend with respect to the increment of cutting speed. The microstructure and mechanical properties transformation in the machined surface of PM superalloy was revealed in order to identify the mechanism of machined surface integrity, it can be provide the theoretical basis for the controlling of machined surface quality.