The ridgetron cavity is the most important part of the ridgetron accelerator. The electromagnetic field of ridgetron cavity was Simulated and optimized according to the radio frequency performance in this paper. The extended electrode should be cancelled to increase Q value and shunt impedence. The mechanical parameter was opti- mized by using the method of parameter sweeping with constraint variable （PSCV）, and the most optimized or rational mechanical parameter was found in the condition of the fixed resonant frequency of cavity. The study result shows that the shunt impedence can increase with the acceleration times in the ridgetron cavity.