Abstract: Unmanned Mars sample return mission is of great significance to obtain scientific results and improve engineering ability. The mission period is longer and technical risk is higher compared with several foreign Mars landing and roving missions. The top-level system design is determined by the mission flight mode. The rendezvous capture and sample transfer process should be completed near the Mars orbit. Therefore, two probes with different functions are required:one is used to perform Mars capture, sample storage and Mars-Earth transfer, the other to complete EDL process, Mars surface ascent and sample delivery. Such key issues as EDL mode, Mars ascent vehicle, Mars orbit rendezvous and capture, sample transfer, earth entry vehicle, system scales, rocket selection, etc. are analyzed in this paper. The main technical difficulty and solution approaches are discussed.