The existing maintainable spacecraft costs a lot to realize the maintainability， and the technical development path is not clear， so it is difficult to popularize and apply. Based on the analysis of the technical characteristics of foreign maintainable spacecraft， this paper puts forward a general design method for maintainable spacecraft from three aspects： maintainable architecture， replaceable functional module architecture and plug-and-play interface architecture. Combined with the proposed method， a modular maintainable satellite with variable main structure configuration is designed， and the key technologies involved are described. The designed serviceable satellite takes the open mechanical system with variable configuration， distributed heterogeneous network system and refillable propulsion system as the core architecture， and the two-level functional modules and three-level interfaces as the repairable carrier. It realizes the maintainability at low cost， reduces the capability requirements for maintenance operators， and the system function and performance can evolve dynamically with the technology development. The proposed method and typical design case could provide reference for the development of maintainable spacecraft and corresponding technologies in China.