The high absorption characteristics, the complex mechanism and the great potential application in detectors of micro-structural material aroused extensive attention. In order to understand the impact of the micro-structure, the optical simulation method based on Monte Carlo is used for reflection characteristics of micro-structural material with the cell of pyramid construction. In this simulation, the body material is made of gold, which can avoid the effect of tranmittance, with a number of 400 cells. The bottom square of each structure is 50×50 µm, and the height of cells is adjustable. Then the relationship between the height and reflectance can be built up. However, a very complex relationship between the reflectance and the input parameters, including refractive index, extinction coefficient and the structure of the material is showed from simulation result. Generally, the reflectance decreases while the height increases.