Photodetectors operating in the visible and near-infrared bands are an indispensable part of various applications, such as optical communications, deep space exploration, and biomedical imaging. We introduce metal nanostructures on a thin layer of graphene to improve the performance of photodetectors. We use COMSOL to establish multiple sets of models for simulation comparison. The results show that at a period (P) of 250 nm and particle diameter (D) of 112.5 nm, the addition of pyramid nano-metal particles and a triangular cross-section grating enhances the light absorption of the graphene photodetector in the visible and near-infrared bands. In the wavelength range of 0.5-5 μm, the nanoparticle grating structure can further improve the absorption performance of the device. The results indicate that particle coverage is the key factor affecting the light absorption efficiency.