In this paper, the DEFORM simulation software is used to simulate the cutting process of AIGI52100 hardened steel with high speed and hard turning of diamond tools. The influence of cutting speed, feed rate and cutting depth on cutting force is studied by orthogonal simulation experiment. The optimal processing parameters combination in the experimental range is given. When the cutting speed is 120m/min, feed is 0.10m/min and cutting depth is 0.10mm, the minimum cutting force is obtained. The empirical model of cutting force is established by using regression analysis method., It is shown that the empirical formula is reliable by taking significance test.