Machining deformation of aircraft monolithic component is simulated by finite element method (FEM) and validated by experiment. The initial residual stress in pre-stretched plate is generated by simulating quenching and stretching processes. With a single tool-tooth milling process FEM, the machining loads in monolithic component material removing is obtained. Restart-calculation is put forward to complete the whole simulation of machining process. To verify the FEM result, an experiment is carried out. The deformation distribution of the monolithic component resulting from FEM shows a good agreement with the experiment result, which indicates that the key technologies presented in the paper are practicable and can be used to simulate the milling process of monolithic component to predict its deformation. Lengthy and expensive trial and error experiment process can be avoided.