The feasibility of a spaceborne lidar system for global CO2 concentration and aerosol detection is studied. As the atmospheric backscatter signal is weak, the spaceborne lidar is very sensitive to stray light. The lidar system is composed of Ritchey-Chretien receiving telescopes, multi-band relay optical systems, and photodetection systems. Therefore, compared with conventional imaging optical systems, the analysis and suppression of stray light of the lidar system can be improved. Based on the modeling of opto-mechanical structures and the classification of stray light sources and a large number of ray traces, a stray light suppression method is proposed in the laser lidar rear-optical system rather than in the receiving telescope. The simulation results show that the baffles in the collimator lens barrels in rear-optical system largely suppresses the stray light. Therefore, the baffles in the receiving telescope should be removed.