In this paper, by adopting an equivalent geometry model of the cutting layer, a three-dimensional (3D) finite element model was built to investigate the milling of Ti-6Al-4V. The chip separating process was simulated by Arbitrary Lagrangian-Eulerian (ALE) method and automatic re-meshing technology. The experiments of milling Ti-6Al-4V were carried out to verify finite element model of milling process. The comparisons of the predicted cutting forces and the measured forces showed reasonable agreement. Finally, the finite element model was used to predict the chip deformation and the three-dimensional distribution of cutting force, stress and temperature in milling Ti-6Al-4V.