As a noncontact, fast, robust, high-sensitive and area-averaging technique, the light scattering containing the structural information of optical surfaces has been used to measure surface roughness for many years, and the high resolution makes it feasible to measure the surface imperfection of silicon substrates. In this paper, using the total scattering (TS) instrument at 633nm, the total scattering was measured by scanning the entire surface of silicon substrates in different surface finish levels and sizes. Then, the root-mean-square (RMS) roughness of silicon substrates was calculated according to the measured TS-values and compared to the measured results with atomic force microscope (AFM) or optical profiler, indicating the validity of the method of light scattering for estimating the RMS roughness of optical components. In addition, the silicon substrates of different surface finish levels were scanned, and the results reveal that the higher the finish level is, the larger the total scattering is. Finally, the scatter maps of silicon substrates were plotted based on the measured TS-values, and the surface defects of silicon substrates were observed and compared to the results observed with an optical microscope, indicating that the spots with larger scattering correspond to the surface defects. It can be shown from our results that measuring light scattering is an effective method to investigate the surface quality of optical components.