The optical surface of sub-wavelength grating structures has anti-reflection characteristics, which are of great significance for the application of photoelectric conversion efficiency. In order to improve the absorptivity of silicon-based grating structures in the near-infrared band (0.78-2.50 μm), we add Ag nanoparticles and an Al₂O₃ dielectric layer to the gap of the silicon surface grating. Furthermore, the FDTD software is employed to investigate the influence of different composite structures and particle diameters on the light absorptivity and analyze the light intensity distribution of the characteristic section in the composite structure at different working wavelengths. The experimental results show that in the context of a line/space ratio of 1∶1 and a period of 1 μm for the grating, as well as two-layer Ag particles (diameter of 0.25 μm) cover with an Al₂O₃ dielectric layer in the periodic groove, the average absorptivity of the composite microstructure in the near-infrared band can theoretically reach 0.463, achieving absorption enhancement. It follows that the metal-silicon gratingdielectric layer composite structure can enhance light absorption, in the application of photoelectric conversion devices, thereby improving photoelectric conversion efficiency.