In this paper, a new mathematical model and modeling method of ball-end milling cutter which satisfies the request of physical simulation in virtual NC machining system are proposed. The accurate expressions of the cutting edge are presented. The precise functional surface model of ball-end cutter is developed. And the 3-D visualization for ball-end milling cutter in virtual NC machining is implemented. The model can provide necessary and accurate geometric information for physical simulation and has been applied in milling force simulation. It laid the foundation for integration of geometric simulation and physical simulation.