In view of a primary mirror of an optical system, the influence of the mid-and-high frequency errors on the Ratio of Scattering Loss (RSL) was analyzed. On the basis of the statistical optics theory and Harvey-Shack scatter theory, a mathematical model of the relationshop between the Root-mean Square (RMSs) of mid-and-high frequency errors and the RSL was established by assuming the surface errors as a stationary Gaussian random process, and the numerical computation and actual surface profile data of the model were validated. It is found that the RSL increases almost in exponential form with the increase of RMS and the mathematical model agrees with the simulation results very well within the focused radius. The influence of the mid-and-high frequency errors on the RSL is less than 1% when the RMSs of the mid-and-high frequency errors are less than λ/63 respectively.The analysis results provide the support for correction of the mid-and-high frequency errors.