The invention relates to a spacecraft data storage system and an access method, and belongs to the technical field of spacecraft data storage and on-orbit maintenance. The important parameters of a spacecraft are linearly stored according to the hierarchical structure so that the complexity of important data management work of the spacecraft can be effectively reduced, and the important data searching and modifying efficiency is improved. The system occupies a small memory space, and is suitable for the spacecraft with very limited storage capacity. According to the system provided by the invention, on-orbit modification of the file content can be carried out through a simple remote control instruction, two on-orbit modification modes of local modification and overall modification of the file system are supported, and convenience is brought to use of a ground user. The system technology provided by the invention is already used and verified in an on-orbit spacecraft in China.