A synchronous communication method, comprising: obtaining , by a first terminal, first configuration information, wherein the first configuration information comprises a first parameter, wherein the first parameter includes an offset; wherein when the first terminal is beyond a network coverage, the first configuration information is obtained in a pre-configuration manner; or when the first terminal is within network coverage, the first configuration information is obtained by receiving system broadcast information or radio resource control (RRC) signaling from a base station; determining , by the first terminal according to a global navigation satellite system, GNSS, clock, a transmission timeslot in a device-to-device, D2D, communications system corresponding to a current moment, wherein the corresponding transmission timeslot in the D2D communications system is a frame number and a subframe number in the D2D communications system; determining , by the first terminal according to the transmission timeslot in the D2D communications system and the offset, whether the current moment is a synchronization information sending moment; and if the current moment is the synchronization information sending moment, sending, by the first terminal, sidelink synchronization information at the synchronization information sending moment, wherein the sidelink synchronization information carries indication information, the sidelink synchronization information is used to synchronize a second terminal with the first terminal, and the indication information is used to indicate, to the second terminal, that the first terminal is a synchronization source that uses the GNSS clock. obtaining , by a first terminal, first configuration information, wherein the first configuration information comprises a first parameter, wherein the first parameter includes an offset; wherein when the first terminal is beyond a network coverage, the first configuration information is obtained in a pre-configuration manner; or when the first terminal is within network coverage, the first configuration information is obtained by receiving system broadcast information or radio resource control (RRC) signaling from a base station; determining , by the first terminal according to a global navigation satellite system, GNSS, clock, a transmission timeslot in a device-to-device, D2D, communications system corresponding to a current moment, wherein the corresponding transmission timeslot in the D2D communications system is a frame number and a subframe number in the D2D communications system; determining , by the first terminal according to the transmission timeslot in the D2D communications system and the offset, whether the current moment is a synchronization information sending moment; and if the current moment is the synchronization information sending moment, sending, by the first terminal, sidelink synchronization information at the synchronization information sending moment, wherein the sidelink synchronization information carries indication information, the sidelink synchronization information is used to synchronize a second terminal with the first terminal, and the indication information is used to indicate, to the second terminal, that the first terminal is a synchronization source that uses the GNSS clock. <EOS>