Proton-irradiation-induced defects threaten seriously the stable performance of GaN-based devices in harsh environments, such as outer space. It is therefore urgent to understand the behaviors of proton-irradiation-induced defects for improving the radiation tolerance of GaN-based devices. Positron annihilation spectroscopy (PAS) has been used to study proton-induced defects in GaN grown by HVPE. The result shows that VGa is the main defects and no (VGaVN) or (VGaVN)2 is formed in 5 MeV proton-irradiated GaN. Photoluminescence (PL) spectrum is carried out at 10K. After irradiation, the band edge shows a blue-shift, but the donor-acceptor pair (DAP) emission band and its LO-phonon replicas is kept at the original position. The intensity of yellow luminescence (YL) band is decreased, which means that the origin of YL band has no relation with VGa. The increased FWHM of GaN (0002) peak in proton-irradiated GaN indicates a degradation of crystal quality.