The present disclosure discloses a method and a communication system for time synchronization. The system includes at least one base station, an optical line terminal OLT, and a fiber for transmitting information between the base station and the OLT. The system further includes a clock synchronization server, configured to transmit synchronization data between the clock synchronization server and the at least one base station, so that time synchronization is implemented between the at least one base station and the clock synchronization server. According to the solutions provided by the present disclosure, the system apparatus is simple, and the cost low.