The present invention discloses a method of time synchronization and a base station system. The base station system includes a main unit, at least one radio unit, and a transmission medium adapted to transmit information between the main unit and the at least one radio unit. The base station system further includes a clock synchronization server configured close to the side of the at least one radio unit or integrated with the at least one radio unit. The clock synchronization server is adapted to transmit synchronization data to the main unit through the transmission medium, so that the main unit performs configuration processing according to the synchronization data to implement time synchronization with the clock synchronization server.