Abstract In order to study the micromilling mechanisms, FEM (finite element method) has been used to create models and to conduct simulations for micromilling process. The aluminum alloy material 7075-T6 is selected as the workpiece material for its advantages to make miniaturized components. By analyzing the variation of the milling force and the chip formation in this simulation, the result shows that the critical process parameter of the MUCT (minimum undeformed chip thickness) is that the feed engagement fz=2μm/z. Simulations with different radial depth of cut ae have been conducted. According to the chip formation and the cutting force, it can be noticed that the milling force increases with the increase of the radial depth of cut. This study lays a theoretical foundation for further optimizations and experiments of micromilling.