Abstract: In order to improve the measurement accuracy of the microwave system for measuring gas,the vents and the hole-coupling slot of the resonator cavity are optimized to address the weak performance for frequency selection of the microwave resonator cavity used as the main measurement component in this system.The cylindrical resonator cavity is designed to operate at 9.6 GHz.The TE₀₁₁mode is excited from the side wall of the cylindrical cavity using a rectangular waveguide by the hole-coupling method.Based on the established resonator system model,ANSYS Electronics Desktop software is used to simulate the cavities with different slot sizes,vent sizes,and vent angles.According to the S-parameters and Smith charts of simulation results,the optimal coupling type of the resonator cavity system is obtained.The simulation and experimental measurement results show that when the slot radius,the inner radius of the top walls,and angle of the vents are 1.96 mm,32 mm,and 150 deg,respectively,the microwave resonator cavity has the best performance for frequency selection.