摘要： Paschen’s curve which is based on Townsend effects has been used to describe the gas breakdown voltage until more and more experiments has shown that it is not entirely accurate in describing breakdown when the electrode gaps less than 10μm. Thus it is of great significance to study the microscale gaps breakdown law and the discharge mechanism of insulation structure in micro-electronic components. In this work, numerical experiments using the particle-in-cell/Monte Carlo collisions method are used to simulate the process of microgap discharge in the air. The variation of the number of charged particles, the current intensity and the electric field distribution are taken as the criteria of breakdown to analyze the breakdown characteristics in microgaps and the points of time determined by different criteria are basically the same. Furthermore, field emission and thermionic emission have different contributions to the entire electron emission from the cathode under different applied voltages and cathode temperatures. The series of experimental results can provide further theoretical guidance for the physical mechanism of microscale dielectric breakdown.