The characteristic and method of the synchronous transmitting function in RPR asynchronous network was introduced. Then a new synchronous transmitting mechanism for RPR asynchronous network according to the principle of allocating bandwidth was proposed. The new mechanism was named as Dynamic Weighted Transporting Rate. The synchronous transmitting wass based on dynamic altered transmitting weight of the received data stream according to the PTQ depth. Simulation results show that the mechanism can achieve synchronous transmitting in RPR asynchronous network,and the PTQ will not overflow.