The performance of optical systems is obviously affected by the surface defects of optical components in terms of losses and image degradation. In this paper, the feasibility of characterizing surface defects of Silicon substrates was investigated by the total scattering (TS) and absorption. The TS values of three Si substrates with different surface finish level were obtained by using the total scattering measurements at wavelength of 633nm. The surface roughness was analyzed by the atomic-force microscope (AFM) and the number of 1μm diam defects in a beam spot was recorded by the optical microscope. Additionally, the scattering value of 1μm diam defects was determined by the ratio of the different value between TS value and the scattering value induced by roughness to the number of the defects in a beam spot. Furthermore, based on the Mie scattering theory, the theoretical value was calculated and was compared with the measured results. The results show that both the theoretical and measured results have the same order of magnitudes. What’s more, in order to study the absorption, the absorption of four samples that include three Si substrates with different finish level and one Si substrate with a high reflector coating were measured by using the surface thermal lensing technique. The experimental results reveal that the poorer the finish level is, the more the number of surface defects is. Finally, the absorptance mapping of the high reflector was plotted and compared with the results observed by the optical microscope and the results indicate that the absorption measurement is an effective method to characterize the surface defects of Si substrates.