In the high-speed cutting, the severe plastic deformation and extremely high cutting temperature tend to cause the microstructure defects of the machined surface, which become the potential risk of fatigue fracture in the process of workpiece service. In this work, the microstructure evolution and formation mechanism of the machined surface for high speed machining GH4169 superalloy were studied combined experiment and finite element simulation. The high speed orthogonal cutting experiments were carried out, and electron back scattering diffraction (EBSD) technique was used to observe the microstructure of the machined surface material. Then, the finite element analysis model of high speed orthogonal cutting of GH4169 superalloy was established based on the modified Johnson – Cook constitutive model. The temperature field and strain field of machined surface material were obtained. The results show that the temperature, strain, and microstructure of the machined surface materials present a significant gradient distribution, and the grains of the nearsurface materials are refined to nanometer level. The gradient distribution of the machined surface material microstructure is caused by the gradient distribution of the force-thermal loads generated in the cutting process.