Passivation can improve the service life of the cutter, the stability of the cutting process and the quality of the machined surface. The edge of passivated cutter is not a regular arc. This paper used the method of discretizing the cutting edge axially into micro element cutting edge and was based on the basic theory of slip line field. Comprehensively considering the variation of ploughing force with cutting thickness and the characteristics of asymmetric edge shear, it pointed out the different cutting stages experienced in the cutting process of asymmetric edge cutter, and established the instantaneous milling force model of asymmetric edge cutter. Finally, a comparative analysis was carried out combining with milling experiments. The results show that the proportion of ploughing force decreases with the increase of cutting thickness in the whole cutting process; the milling force obtained from the model well accords with the experimental results. The correlation coefficient of the two is greater than 0.7, the ave-rage error is less than 5%, and the peak error is less than 15%.