With the development of spaceflight technology, the demands of data exchange capacity and real time between satellite and earth are more and more prominent. The traditional spacecraft information system is based on 1553B bus or RS422 and LVDS, and transmits data at most at 1 Mb/s or 100 Mb/s, which cannot meet the requirement of real-time data transmission. In this paper, a new system design method is proposed. The method applies the mature 1 000 Mb/s/10 Gb/s Ethernet technology to the spacecraft to construct the integrated communication network, greatly improve the data transmission rate and reduce the weight of onboard cables when the total bandwidth of wireless link is allowed. The method has been successfully applied in a large combined spacecraft mission, and can be a reference for the future spacecraft data transmission system design.