Provided are a synchronisation method, a terminal device, a network device and a storage medium, capable of ensuring synchronisation between a terminal and a satellite system via D2D means. In the method, a network device determines that a first terminal cannot synchronise with a satellite system; the network device instructs a second terminal to send a satellite system-based synchronisation signal, used for the first terminal to synchronise with the satellite system via the synchronisation signal. In a possible implementation, the method may include that: the network equipment receives a first message sent by the first terminal, the first message indicating that the first terminal is not able to be synchronized with the satellite system and the first message including information configured to acquire the present position of the first terminal.