Basedon finite element simulation,the microstructure changes during machining TC4 alloy under dry cutting condition and cryogenic cutting condition were studied. Based on the user defined programmer,the constitutive model, the properties of the microstructure of the alloy under different cutting conditions, and the flow stress ofmaterial under cutting conditions were defined.So that the stress values of material can be updated at any time according to the calculating results. At last, the simulation results were validated as correct by the experimental results.