Peer-to-Peer P2P applications consume most of Internet bandwidth and cause access network congestion. They severely deteriorate the performance of the traditional Internet applications. Previous researches have studied the mechanisms to improve the aggregate throughput of P2P traffic, but there doesn’t exist any research to predict and quantify its impact. In this work, we develop a performance modeling system of P2P file sharing traffic and traditional Internet traffic (WEB traffic) to quantify the impact of P2P file sharing traffic on WEB traffic in the congested access network. We answer the following questions from a user’s point of view: How many P2P concurrent connections and what proportion between P2P traffic and WEB traffic will guarantee certain WEB performance. The simulation results demonstrate that our model is accurate and efficient.