Abstract: The theory model of STIM simulation is reported here.A related computer program which runs on Windows 9X/NT is written by the fourth generation Object-Oriented Programming (OOP) language C++.With its friendly interface,some parameters can be easily changed,such as detector resolution,scanning scale and elemental distribution of specimen.Automatically 360° rotation can be achieved and any rotary angle in experimental condition can be simulated.With multithread processing,the program runs faster and can be paused or stopped at any moment.The result of some examples are showed and discussed.