A method of controlling the rate of long-duration large flows and its performance evaluation is described in this paper. Most conventional QoS controls allocate a fair-share bandwidth to each flow regardless of its duration. Thus, a long-duration large flow (such as a P2P flow) is allocated the same bandwidth as a short-duration flow (such as data from a Web page) in which the user is more sensitive to response time. As a result, long-duration flows will occupy the bandwidth over the long period and worsen response times of short-duration flows, and the conventional QoS methods do nothing to prevent this. We have, therefore, proposed a new form of QoS control that takes flow duration into account and assigns higher priority to the acceptance of shorter-duration flows. In this paper, we show through simulation that our method achieves high performance for short-duration flows without degrading the performance of long-duration flows. We also explain how to set parameters used in our method. Furthermore, we discuss the applicability of a packet-sampling technique to improve the method's scalability.