With the development of IP-based 3G network and services, packet transport network (PTN) technology has been developing rapidly since it was proposed in 2008. PTN needs to synchronize the time, and transmit the time synchronous information to each node in the network. Currently PTN mainly transports high-precision time information between different sites which are accord with IEEE 1588v2 protocol. However, in practical situation, the transport networks mostly are bi-directional optical fiber network. As the fiber lengths in transmit end and receive end are quite different, it means the transport link will be asymmetric. And this would surely affect the accuracy of time synchronization as per IEEE1588 V2. To solve this problem, we have put forward corresponding solutions to carry out on-site measurements according to the actual network situation.