Cutting force is an important parameter in machining. The static balance method and experience formulas had been adopted to find its value, but the theoretical calculated value is not good agreement with the experimental value for the same set of cutting conditions. In practical machining, the cutting tool has obvious impact effect on workpiece, so a dynamics analytical model for cutting process is established in this paper. Based on the proposed solution, a new formula for cutting force has been obtained. The suggested formula has shown to correspond well with the experimental data.