A traffic management device and the method thereof are disclosed. The traffic management device includes a control logic unit, a first counting unit, and a second counting unit. The traffic management method follows the dual leaky bucket mechanism. A first count value and a second count value are generated by the first counting unit and the second counting unit, respectively, such that the control logic unit controls the average rate by checking whether the first count value falls within the range of a first threshold and controls the peak rate by checking whether the second count value falls within the range of a second threshold. When both the conditions are satisfied, packets in the queue are transmitted. Thus, the network flow is controlled effectively.