Aiming at the problem that the tool is easy to wear and tear that causes sharp fluctuations in cutting force， which makes the milling process difficult to control， the precise cutting force element that takes into account the frictional characteristics between end mills and chips needs to be established. Based on that the fixed friction coefficient can not fully describe the friction characteristics during the milling process， taking carbide end mill milling process of Cr12MoV hardened steel as the research object， an empirical model of friction factor is established according to the temperature distribution of rake face and the relative slip velocity between the cutter and the chip. Based on the material hardness， the milling force prediction models of the first shear zone， the second shear zone and the third shear zone are established respectively. Then a three-dimensional milling force prediction model of the end mill is considered with the help of discretization. The simulation results are in good agreement with the results measured by the milling experiment， which verifies that the established model has high prediction accuracy， and further proves that the milling force increases with the increase of the flank wear width. The results provide theoretical support for the optimization of high hardness die steel milling.