Based on geometrical structure of retroreflector and vector form of reflection-refraction law, a mathematical model with EDR is built up for retroreflector.By the means of numerical simulation, the regularity of change for EDR and the impaction of regularity on far field diffraction intensity (FFDI) are analysed. The simulated results show that EDR decreases with the increase of the divergence of FFDI with laser incidence angle.But,laser amuzith has no impact on shape of EDR and total diffraction intensity,which only makes their distributions rotate amuzith angle. When atmospheric effects are ignored,In terms of FFDI distribution with different incidence condition and velocity aberration theory, the new way for designing retroreflector radius is put forward.The investigation of EDR provides important approach to calculate FFDI and design satellite retroreflector.