The numerical controlling simulation of process indicates a mapping of NC machine tool in the virtual environment, and it includes the technique of manufacture, the theories of NC machine tool, CAD, CAM, and the technique of modeling and simulating. The people can apperceive the virtual environment of 3D simulated model developed by computers, carry the NC process of parts in virtual condition before the true doing when we design or alter a project, inspect the exactitude and justification of NC program, evaluate and optimize the project of process. Thereby the intention, abridging the time of developing products, depressing the cost of manufacture, advancing the quality of products and the efficiency of Production, can be finally achieved. With the rapid development of NC technique and computer graphical technology and the extensive application of computer, NC simulation technology provide an effective tool in order to validate the NC machining program and forecast the machine process. The main purpose of this dissertation is to derive the mathematical model and to simulate the lathe tool cutter. In order to enhance the operating efficiency and the demonstration quality of the numerical control lathe simulation software, the analysis has compared a kind of shape about lathe tool cutter-- PARALLELOGRAM, has established the cutter forms, thus inferred the mathematical model of the numerical control lathe simulation on the lathe tool cutter. The cutter is display in the DELPHI software development platform based on the environments of GLSence using this derived mathematical model.