According to the requirements of time synchronization in long haul optical fiber links, the bidirectional Erbium doped fiber amplifiers(EDFA) are used to extend the transmission distance. This paper introduces the composition of the optical fiber time transfer system. By constructing the time delay model of the optical fiber time transfer link, it focuses on the research and analysis of the asymmetric time delay in the long-distance optical fiber time transfer system, and details the accurate calibration method. Finally, an experimental platform is built to test and verify the time transfer performance. The test results show that the time synchronization accuracy is -47 ps, and the synchronization accuracy is 128 ps, the 600 km sub nanosecond optical fiber time transmission is realized.