The tool wear is serious in the process of machining difficult-to-machine materials. The tool wear will directly lead to the change of milling force. Therefore, a milling force model considering the flank wear of ball end milling cutter is proposed. In this model, the milling force is decomposed into shear force produced by the shear effect of the rake face, and the friction force and pressure of the flank surface. Taking the axial position angle of the cutting edge of the micro element as the parameter, the milling force model considering the wear of the flank surface is established, and think that the axial milling force of the cutter is not affected by the friction effect. Finally, the cutting tool wear experiment and milling force experiment show that the experimental results are consistent with the predicted results, and verify the correctness of the milling force model is verified. It provides effective guidance for optimizing the technological process and improving the surface quality.