During the metal cutting process，the intense thermo-mechanical load can cause changes in the microstructure of the chips． In order to reflect the influence of the material microstructure on the mechanical behavior of shear zone，an analytical model of microstructure evolution in shear zone based on dislocation density was proposed． And it was used to model the microstructure evolution process caused by plastic deformation during chip formation． Firstly，the distribution of strain and strain rate in shear zone was calculated through the analytical model of unequal shear zone． Secondly，the Johnson-Cook ( J-C) flow stress model was replaced by the material model based on dislocation density to calculate the temperature field in the shear zone iteratively． Finally，the evolution process of dislocation density and grain size in shear zone of orthogonal cutting oxygen-free copper and aluminum alloy was simulated． The results show that the analytic model for the micro-evolution of the shear zone combined with the dislocation density can better reflect the basic characteristics of the deformation field and microstructure evolution during the cutting process． The predicted values of cutting force and grain size in chips under different cutting parameters are in good agreement with the experimental data．