Porous GaN thin films were successfully prepared by high-temperature annealing of GaN thin films with Au nanoparticles deposited on their surfaces in H2 and N2 atmosphere. The surface morphology of the porous structure can be regulated by parameters such as annealing temperature, annealing time and Au deposition time. The crystal quality of different GaN structures was characterized by high-resolution X-ray diffraction (HRXRD) and Raman spectroscopy. Compared with planar GaN, the dislocation density and residual stress of porous GaN are reduced. When the annealing temperature is 1 000 ℃, the dislocation density is the lowest and more compressive stress is released. The optical properties of the porous GaN were characterized by photoluminescence (PL) spectroscopy. Compared with planar GaN, the luminous intensity of porous GaN is significantly improved, which can be attributed to the increased porosity of the porous structure, and therefore effectively increased light scattering. In addition, the photocurrent density of different GaN structures was tested by electrochemical work station, and the results confirm that the photocurrent density of porous GaN with larger specific surface area can be increased by about 1.67 times when used as a working electrode. Porous GaN thin films through high-temperature etching are successfully prepared in this paper, which providing some theoretical guidance for the improvement of the crystal quality and optical properties of the GaN epitaxial layer, and also shed some light on its application in the fields of photoelectric catalysis.