Performance of optical systems is closely related to the scattering characteristics of optical mirror surface. According to Mie theory, the bidirectional reflectance distribution function of optical mirror surface under four cases of mirror surface cleanliness levels such as clean, basic clean (cleanliness level 200), slight pollution (cleanliness level 500) and severe pollution (cleanliness level 750) was simulated and computed by MATLAB software when incident laser wavelengths are the visible light (0.632 8 μm), near infrared light (1.053 μm) and thermal infrared light (10.6 μm), respectively. The results show that the bidirectional reflectance distribution function of mirror surface is affected by mirror surface roughness and clean lines level, which will make a very important impact on properties of optical system. If wavelength is shorter, bidirectional reflectance distribution function will be greater, and scattering becomes more complicated. Useful help will be provided to estimate the pollution of optical mirror and clean the mirror surface in optical engineering.