The invention provides a data transmission system. The system comprises a first sub data transmission system and a second sub data transmission system; the first sub data transmission system comprisesa first exchange unit, a second exchange unit and N first hub devices; the first exchange unit comprises a second hub device and N first exchangers; the second exchange unit comprises a third hub device and N second exchangers; each first exchanger and the second exchanger corresponding to each first exchanger are respectively in communication connection with one first hub device; the second subdata transmission system comprises a third exchange unit, the second exchange unit and N fourth hub devices; and each third exchanger and the second exchanger corresponding to each third exchanger arerespectively in communication connection with one fourth hub device. By means of the data transmission system provided in the embodiment of the invention, the wiring number of the system can be reduced.