Abstract: The displacement damage induced by 1, 5, 10, 20, 50, 100, 500, 1000 MeV protons in GaAs was simulated with the Geant4 software. It’s found that the number and variety of PKA increase with the incident proton energy. And with the increase of incident proton energy, the PKA energy spectrum has a decrease variation, and the proportion of PKA at low energy range is reduced, while that at high energy range is raised. Simulation results show that the defect concentration has a typical Bragg’s distribution along the proton incident path.