Aiming at the problem of tool wear and breakage， the low accuracy of machined surface during the milling process of automobile panel splicing dies, the cutting force modeling of micro element is carried out. The cutting chip thickness of each cutting cycle is built as a function of the cutting angle and the shear force according to the different hardness of machining materials, and a plow force model are obtained under different cutting angles. By introducing a single-degree-of-freedom italic collision model, the Hopkinson test is used to obtain the elastic deformation of the tool-workpiece impact under different spindle speeds, and then the impact force on the tool in the transition area is obtained. Combining above models together, the prediction model of milling force in the transition area can be obtained. Experiment and simulation results show a good consistency to prove the accuracy of the model. The surface quality under different feed directions is studied. From the analysis results of machined surface quality, surface roughness and height difference between workpieces, it is concluded that better surface quality can be obtained from high hardness and low hardness workpiece. The results provide theoretical support for the optimization of the milling process in the splicing die of the automobile panel.