To enhance the absorption of light using a wavelength of 1550 nm using a photodetector device in a communication system, we propose a composite micro-nanoscale structure including a silicon grid, nanoscale silver balls, and a buffer layer. The light absorption of the composite micro-nano array can be improved by means of the local field enhancement effect of surface plasmon resonance on metal and the trapping effect and coupling effect of silicon gate. The finite difference time domain method is used to calculate the light field distribution of the simulated light passing through the silicon grid composite micro-structure array filled with silver nanospheres and alumina. Then, the effect of the silicon column array duty ratio, the silicon column side length, the silicon column height and the filler on the absorption performance are analyzed. The simulation results show that when the silicon gate line or interval, silicon column length is 800?1000 nm, the diameter of the silicon column gap filling nanometer arguably is half of gap width and covered with clearance and covered in alumina, at the bottom of the composite structure of the absorption rate with high silica column array cycle and the column of different can reach 0.2288?0.5753, the near-infrared wavelength of 1550 nm have significantly enhanced absorption effects.