Abstract: Synthetic aperture ladar(SAL) is a kind of high-resolution active imaging ladar, which operates under day and night and long distance conditions. Taking the platform of lunar satellite Chang'e-1 as an example, several problems about SAL were ananlyzed based on lunar surface imaging. Then, using the theory of statistical optics, the statistical characteristics and signal-to-noise ratio of detect signal in photo- limited regime were analyzed. Finally, the related parameters and total number of photons of SAL system was derived based on the lunar satellite platform and it was proved to be feasible in theory.