Abstract: Advances in computer technology and software design have enabled the concept of Virtual Simulation (VSIM), first suggested by George Sherouse, to be realized. VSIM is a technique involving the use of medical image data to construct a 3D virtual patient model which is used for the design and implement of radiation treatment. CT-based virtual simulation, the so-called CT Simulation (CTSIM) has become an integral part of the application of VSIM in modern radiotherapy. High precision of proton therapy made this technique even more prominent. The procedures and the whole process of simulation used in our proton center were described, the advantages as well as disadvantages of this technique were also discussed.