Submarine is an important part of modern military power, and communication with submarine is a key problem which needs solving. Blue-green laser communication system with submarine can improve the safe depth and communication speed of submarine greatly, and many countries have paid a lot of attention to develop laser communication system for a long time. The disturbance would communicate in the whole system if the stray lights exit and influence the signals on detector focus surface, and these will increase the BER and influence the communication ability. This optical receiver system adopting Ritchey-Chretien(R-C) Cassegrain structure of blue-green laser communication system with submarine is introduced firstly in this paper, and then the sources of stray light are analyzed detailedly. The corresponding elimination methods for stray light are proposed and according to the analysis, the further optimization can be carried out.