关键词: 无结构化P2P，搜索方法，本地索引，层次，聚集

Abstract: The success of file-sharing applications such as Napster and Gnutella makes Peer-to-Peer networks developing rapidly. Efficient resource discovery is the first step towards distributed resource sharing. Recently many search methods have been proposed. We gave an overview of search mechanisms for unstructured Peer-to-Peer networks in this paper. Firstly we approximately classified existing search methods based on the features of them. Then we discussed　critical techniques used in these approaches in detail and compared the performance of them on various metrics, giving emphasis on the success rate, message production, adaptation to dynamic network conditions and maintenance overhead.Finally recommendations were given for future work.

Key words: Unstructured P2P, Search method, Local index, Hierarchy, Clustering