The statistical characteristics of a retro-reflector reflecting a Gaussian beam is analyzed, which shows that the retro-reflector can be approximately characterized by an ABCD ray-transfer matrix, and a monostatic system in atmospheric turbulence with a retro-reflector as the target is processed with ABCD ray matrix theory. Analytical expressions are developed for the basic statistical moments, the degree of coherence and the scintillation index of the retro-reflected wave are calculated in terms of three fundamental statistical moments, and then the backscatter amplification effect associated with these properties are discussed. As comparisons, the results of both monostatic and bistatic cases of a plane mirror are also presented. All the results are based on the weak turbulence with von Karman spectrum.