Echo receiving system is an important part in the optical system of frequency modulated continuous wave noncooperative target ranging; and its receiving characteristics have certain influence on the ranging precision of the system. In order to conduct the design and analysis of the system, optical design software was used to conduct the modeling of the receiving system with Cassegrain telescope and multimode fiber as the main body, and the parameters of the Cassegrain telescope were determined through analyzing and optimizing the aberration and optical receiving efficiency. The Gaussian scattering model for the backscattering of the target was established; a complete receiving optical path was built to conduct the experiment; the received power of the system was analyzed quantitatively under different conditions, and the rules between receiving efficiency, focusing position and target distance, surface scattering were investigated. The research results show that for the sample blocks processed with the same method, the system receiving power is negatively correlated with the roughness and target distance, while the system focusing distance is positively correlated with the roughness and target distance.