<p>Distortion is one of the main problems encountered in chemical milling of the thin-walled workpiece. The distortions after chemical milling of bent 2198 Al-Li alloy sheet were measured with different parameters: milling depth and milling area. It was found that the distortion is positive when the milling depth is small and turns to be negative when the depth increases to 40% of thickness. When the milling depth is 25%, the distortion increases with the increasing of milling area. In order to exhibit the evolution of the stress distribution during milling, a calculating model based on FEM is proposed. Firstly, an anisotropic yielding function based on Hill 1948 is established for increasing the accuracy of simulation of bending and springback. Secondly, the chemical milling process is simulated using the birth and death element algorithm. The milling distortion is from the geometric adjustment for the new equilibrium. The distortion is determined by the residual stress integration over the volume of the milled layer. When the milling depth is about 32%, there is not any distortion.</p>