The present invention discloses a method and system for transferring TDM services in GPON, the method includes the steps of: in the case of performing the GPON ranging process, buffering the uplink TDM service data received by an optical signal transceiver in an Input Buffer, reading out and transferring the uplink TDM service data buffered in an Output Buffer. The present invention eliminates the possible interruption of TDM services during the GPON ranging process by buffering the uplink services at the OLT and ONU/ONT side and relevant processes, and therefore realizes the TDM service transmission without any loss during the GPON system ranging process.