In order to analyze the size effect of aluminum alloy Al2024T3 in the micromilling process, the Johnson-Cook thermomechanical coupling model in the nonlinear finite element analysis software ABAQUS/Explicit was used to simulate the sample metal. The simulation results show that the cutting force reaches the minimum value of 0.429 232 N when the feed of each tooth is 0.4 μm/s, which is consistent with the real performance of the size effect phenomenon. The finite element simulation model of the micro 〖JP2〗milling provides some reference cutting elements for micro milling and provides reference for further research on micro milling mechanism.