We demonstrate a type of photoelectrochemical (PEC) self-powered ultraviolet (UV) photodetector using TiO2-modified GaN porous films as photoanode. This nanostructure offers high interface, low charge recombination and efficient electron transport pathway due to the high electron mobility of GaN. Under UV illumination, the assembled UV photodetector exhibits a high photocurrent density of 152.2 μA cm-2, a high responsivity of 0.315 A/W, and a fast response time of 0.03 s for current signal. Moreover, this UV photodetector can also shows visible-blind characteristics and considerable spectral response under weak UV light irradiation. These excellent performances of the GaN-based photoanode will further widen significant advancements for PEC-type self-powered UV-photodetectors.