Abstract: The efficiency of employment will be influenced and the life span of use will be reduced when the material is irradiated and the displacement damage which will change its microstructure and degenerate its character of service is produced within the material. The transport of proton in GaN was simulated with Geant4. The information of the type and the energy of the primary knock-on atoms (PKA) created in GaN and the number of displacement damage were calculated with protons for energy of 1, 10, 100 and 500 MeV. The distribution of displacement damage of 10 MeV proton was calculated. The non-ionization energy loss (NIEL) was studied and calculated for these four kinds of energy protons irradiating GaN and the factors impacting the production of displacement damage were deliberated. The information of the type and the energy of the PKA created in GaN and the number of displacement damage are influenced heavily by the energy of the irradiating proton. The NIEL deposited per thickness of the material decreases along with the increase of the energy of the irradiating proton. The number of the dislocation atoms increases along with the penetration depth within the projected range but will fall tremendously and further reduce when it is beyond the projected range with 10 MeV proton irradiating GaN. The energy of the proton is not the only factor which can influence the interaction between the proton and the GaN.