The defect properties, including defect type, energy level, concentration induced by proton were investigated by numerical simulation. The results indicate that only acceptor-like defects can significantly influence the device characteristics, and the device performances deteriorate more and more dramatically with the increase of defect-concentration. Additionally, the drain current decreases gradually with the increase of energy level with respect to the conduction band, and ultimately saturates at energy level distance of 0.5 eV.