The invention relates to a method, a device and a synchronous system for sending and receiving synchronous information; wherein, the method comprises the steps as follows: a plurality of different groups of long complementary Golay sequence pairs are generated by short complementary Golay sequence pairs; long complementary Golay sequence pairs are selected out of a plurality of different groups of long complementary Golay sequence pairs and distributed to all transmitting antennas; time-domain synchronous sequences are generated according to all selected complementary Golay sequences; orthogonal frequency division multiplexing modulation (OFDM) is carried out on the time-domain synchronous sequences so as to generate OFDM symbols; the OFDM symbols are respectively sent by all corresponding transmitting antennas after cyclic prefix (CP) is added. The method, the device and the system can be used for the synchronization of distribution-typed multi-antenna OFDM systems; adjacent districts are not easy to be disturbed by each other; accuracy of time delaying and frequency offset estimation is improved, the realization is simple and the stability of match performance is high.