Abstract: According to the physical requirements of the medical cyclotron, the specific structure design scheme of the medical cyclotron RF cavity was confirmed. In the case of high accelerating voltage and limited space, the vertical cavity of 1/2 wavelength line was designed for enhancing the cavity quality factor. In order to avoid frequency drift caused by the thermal deformation in the practical work, fine-tuning ring was adopted to meet the requirements of frequency stability. In the paper, the electromagnetic field distribution, quality factor, surface current distribution, coupling capacitance and fine tuning ring of the cavity were analyszed in detail and calculated using Microwave Studio CST program. The results show that their simulated results are agreed with the actual measured values through comparing and the produced errors were analyzed and discussed.