Microplasmas have attracted more and more attention due to their unique characteristics, and breakdown voltage is an important parameter for microplasma devices, particularly for addressable arrays of microplasma devices. However, small changes in shape or interface would bring obvious change in breakdown voltage. In this paper, five groups of simulations of breakdown voltage were operated under different geometry parameters to develop the trend of breakdown voltage following geometrical size under different operation pressures. The drift-diffusion approximation model is adopted in these simulations. The simulation results show that breakdown voltage will increase with the increase in the microcavity depth and thickness of the dielectric. Therefore, the breakdown voltage will reduce when microcavity width increases. The less is the microcavity size, the less is breakdown voltage, and the higher is the pressure corresponding to minimum breakdown voltage, which shows that the decrease in microcavity size can develop operation pressure and decrease breakdown voltage obviously.