Abstract: The problem of the unstructured peer-to-peer system is the scalability of the system due to network traffic cost. This paper presents a new route algorithm of unstructured peer-to-peer system with routing indices. In the algorithm, a peer records the subject which it query about in the past and who can answer the subject. When peers receive a new query, it can forward the query to a selected peer which can answer the subject in the past. In this way the peer reduces the blind search. In the end, we test our design through simulations and the result shows that our design routes the query effectively, and reduces the network traffic greatly, improve the searching success ratio.