Abstract: A cylindrical resonant cavity working on TE11 mode for microwave plasma chemical vapor deposition (MPCVD) systems is designed on the basis of electromagnetic theory. The expression of the electric field distribution in the cylindrical cavity is derived and the geometrical size of the cylindrical cavity is calculated. The electric field distribution in the cylindrical cavity is simulated by using the electromagnetic software CST. The difference of electric field distribution from different coupling depth of antenna and thickness of quartz window is compared. Through the optimized simulation results, it is proved that the microwave power has a good coupling when the coupling depth of antenna and the thickness of quartz glass are both 5mm, and it can satisfy the requirement of industry. After practical processing, the simulation results shows good agreement the actual system's working condition. plasma chemical vapor deposition system, promote the development.