Gallium nitride(GaN)-based high electron mobility transistors(HEMTs)that work in aerospace are exposed to parti-cles radiation,which can cause the degradation in electrical performance.We investigate the effect of proton irradiation on the concentration of two-dimensional electron gas(2DEG)in GaN-based HEMTs.Coupled Schrodinger's and Poisson's equations are solved to calculate the band structure and the concentration of 2DEG by the self-consistency method,in which the vacancies caused by proton irradiation are taken into account.Proton irradiation simulation for GaN-based HEMT is carried out using the stopping and range of ions in matter(SRIM)simulation software,after which a theoretical model is established to analyze how proton irradiation affects the concentration of 2DEG.Irradiated by protons with high fluence and low energy,a large number of Ga vacancies appear inside the device.The results indicate that the ionized Ga vacancies in the GaN cap layer and the AlGaN layer will affect the Fermi level,while the Ga vacancies in the GaN layer will trap the two-dimensional electrons in the potential well.Proton irradiation significantly reduced the concentration of 2DEG by the combined effect of these two mechanisms.