A dual-mechanism cutting force predicting modeling technique was proposed for eight ball end milling operations commonly applied on 3-axis CNC machine tools. The ball end milling was divided into a number of elementary cutting edges. Firstly, the local cutting forces within each elementary cutting edge were analyzed and modeled. Then, total cutting force could be calculated by integral operation. The effect of stepinterval in cutting zones was taken into account for cutting force prediction. The number and distribution of the elementary cutting edges involved in cutting action could be instantaneously determined by geometric analysis. The numerical simulation was implemented by Matlab. Finally, the proposed model was validated through milling experiments of 45# steel. The results showed that there was a good agreement between the experimental results and the simulation ones.