This document Cutting stress coupled with clamping stress and initial stress affects the workpiece deformation. To analyze the workpiece deformation the initial stress model is developed. The finite element model of milling process is established and the milling force and milling heat is predicted. The multi-stress coupled model is developed and the workpiece deformation during machining process and deformation after fixtures released are predicted. This study is helpful to predict and control the deformation for thin-walled workpiece.