Prediction of cutting performance in ball end milling of free form surfaces is increasingly important for selecting the optimum conditions in high speed machining. In this paper, a simulator for ball end milling was developed using a precise cutter model, which consisted of rake and flank faces and chisel edges. Then, the swept volume with the cutter was calculated for each time increment and removed to update the shape of the in-process workpiece. Through this process, the detail topographies of finished surfaces were obtained for different cutting conditions and tool postures. The removal rates of workpiece with rake face and other faces were also calculated at any moment of increment.