Abstract: This paper studies encapsulated packet length of circuit traffic in the multi-service transport multi- protocol label switching network, which based on ITU-T standards. And the paper compared the performance of the network according to different TDM packet length. Then, an adjustment scheme is proposed to change the packet length dynamically. With the consideration of the real-time conditions of the traffics latency and variance, this scheme calculates the suitable payload sizes in the destination node and feeds back to the source node, in order to adjust this size in the adaptation module. This scheme is implemented in a testbed based on OPNET modeler for performance evaluation. The simulation results show that, compared with traditional constant bit encapsulation scheme, this scheme works more effectively both on the transmission quality and efficiency, and meets the requirement of supporting circuit traffic.