Finite element method is an important way to study the cutting mechanism in machining. In the OXLEY analytical model, the shear angle, the shear band widthes of the first deformation zone and the second deformation zone in the cutting process are the important basis for studying the cutting force and cutting temperature. Deform2D cutting model was established, and the shear angle was measured by post-processing interface. Considering the shear strain in the second deformation zone, a new shear angle solution model was established. The new shear angle model had good consistency with the measured shear angle. Finally, the thicknesses of the first and the second shear bands were determined by strain rate and strain distribution nephogram, and the relationship between the thickness and cutting speed and cutting depth was explored.