Light trapping structure in silicon solar cells can produce multi-reflectance of light and improve light absorption. In order to study the effects of micro-structure with different structure parameters on the reflectance of rays for a wavelength range of 300 nm-1200 nm, a numerical algorithm is utilized to trace the propagation path of rays and Fresnel equations are used, and wavelength and incidence are considered to determine the reflectance of every single ray at each reflection point. The weighted reflectance defined as ultimate reflectance for the whole rays projects onto silicon cell is calculated and the light trapping efficiency of micro-structure is analyzed. For rectangular groove microstructure, the weighted reflectance can reach zero theoretically, When primary incidence (defined as the initial incidence of rays when projecting onto silicon solar cells) ep 60, the weighted reflectance is less than 10% for all wavelength rays when rectangular groove structure parameters are in specific range, More intensively, when wavelength of rays are in the range of 400 nm-1200 nm, the reflectance can be smaller than 8% for a refined parameters range.