This application discloses a data transmission system applied to long-distance transmission of data with a large data amount. A plurality of data transmission subsystems connected to each other through a high-bandwidth data transmission link are set in the data transmission system. The data transmission subsystem is further connected to a low-bandwidth data access link, and an apparatus for temporary data storage is further disposed in the data transmission subsystem. In a data transmission process, the data transmission subsystem receives the external data through the data access link, first buffers the external data in the apparatus for temporary data storage, and then transmits, through the high-bandwidth data transmission link, the data buffered in the apparatus for temporary data storage.