Abstract: In order to resolve the issue of containing query with a node set formed by multi-keywords,this paper proposes an index structure,named PS-Tree,and applies it to a semantic search engine.The PS-Tree refers to a set attribute index of object-orient database.It can map user's query to a semantic path which contains semantic relations as the aim of user's query in form of multi-Key words by "range query".It can improve the performance of index structure.The experiment result shows that the PS-Tree gives a good performance especially when there is a long semantic distance between the query Key words.