BitTorrent is one of the most popular P2P file sharing systems. However, chunk-based file sharing mode makes it difficult to detect content pollution and prevent pollution dissemination during downloading process. In this paper, we propose an early warning scheme against pollution dissemination for BitTorrent. Our idea is to build an early cooperative warning mechanism and rapidly spread alert message among peers in the swarm when pollution is detected at the early stage, which is called "early warning, quickly reacting". The performance evaluation based on fluid model shows the necessity and effectiveness of our scheme, which effectively reduces the traffic abusement and restricts pollution dissemination in BitTorrent-like P2P networks. Another advantage of our solution is that it can handle cheating behaviors made by malicious or unconscious peers, which shows the robustness of our solution.