Abstract: With the development trend of high-frequency miniaturization of wireless communication systems, the design of microwave filter is more stringent. As an important index to measure the performance of the filter, the power handling capacity is faced with severe challenges when the filter size is shrinking. The resonator is the basic component of the filter. It is very important to predict the power handling capacity of a single resonator accurately. In this paper, the capacitance-loaded coupling structure is approximated as a parallel plate structure for a coaxial resonator operating at 2.6 GHz in TEM mode. The critical breakdown electric field of the coaxial resonator is obtained by using the single-particle Monte Carlo method, and the low-pressure discharge power threshold of the coaxial resonator is simulated and predicted. The low-pressure discharge experiment of the designed coaxial resonator was carried out, and the experimental curve of the breakdown power threshold with the pressure in the range of 100~1000 Pa was obtained, and the accuracy of the single-particle Monte Carlo simulation prediction method was verified.