Compensation characteristic of coupling efficiency in process of coupling space light into single-mode fiber was studied in the satellite-to-ground link. According to satellite-to-ground link feature, coupling efficiency model was analyzed. Wavefront phase modal compensation model using orthonormal polynomials on pupil weighted by the backpropagated fiber mode field was built. Based on this model, the relation between average fiber coupling efficiency and received aperture diameter or phase modal term compensated was obtained by numerical simulation. The probability distribution of coupling efficiency was given for typical received aperture by using different term modal compensation. The research work can offer a useful reference for compensation system design of satellite-to-ground optical communication based fiber coupling way.