The response of graphene surface plasmon (SP) in ultraviolet (UV) wavelength region and its functional applications on the short wavelength of graphene/semiconductorare both fascinating research areas. Herein, a hybrid structure of graphene/GaN nanofilm was designed and fabricated to investigate the photoluminescence (PL) performance and the coupling dynamics. It is demonstrated that the resonant coupling between graphene SPs and GaN exciton emission is responsible for the substantially enhanced PL from the structure of graphene/GaN nanofilm. The underlying mechanism of the improved PL performance was proposed based on theoretical simulation and experimental characterization. The results are helpful to design new types of optic and photoelectronic devices based on SP coupling in graphene/semiconductor hybrid structures.