In this thesis, a simulation of the AVF type cyclotron magnet for accelerating protons in 10MeV and 30MeV energies has been studied using CST code . The reason for using this type of cyclotron is to achieve a higher energies of protons than the One of the important applications of AVF cyclotrons with 10MeV proto energy is the production of radioisotopes و و for PET imaging. An example of these cyclotrons is available at the Masihe Dashnarsi Hospital in Tthran for the producting of specific radioisotopes for cancer diagnosis. The cyclotron with 30MeV proton energy is used for the production of radio drugs ، ، ، ، ,v . Karaj cyclotron is an example of 30MeV cyclotron which is currently being exploited for medical, industrial and agricultural purposes. our country's need for such accelerators has increased because of the importance of diagnosing and treating cancer. The magnet is one of the most important parts of the cyclotron, which is responsible for directing the beam in a circular path and focussing it. In the AVF type cyclotron, the geometrical characteristics of the valleys and hills in magnets must be designed to create a suitable magnetic field for the optimum conditions .In this thesis, the optimum conditions for 10MeV and 30MeV proton energies were obtained by CST code. For this purpose, diameter of the magnet poles, height, angle of the poles, vertical distance between the poles, ampere-turn and width and height of the wire must be determined. Finally, the dynamics of the proton beam was investigation in the cyclotron.