Theoretical foundation about the workpiece material model simplification and cutting coupled thermal boundary settings of milling numerical simulation to high-strength aluminum alloy was researched, and a large flat milling 3D finite element model was established. The computer simulation was carried out about forming the chip during the material milling, the time history of cutting forces and cutting heat. The causes were analyzed further. Finally, cutting force and cutting heat were taking as the target to optimize the cutting parameters. The results show that cutting numerical simulation method can be used to effectively predict cutting force and cutting heat distribution in the metal cutting process, while the methods can be used for related materials machining simulation and optimization design.