With XML being the standard for data encoding and exchange over Internet,how to manage XML data efficiently becomes a critical issue．An effective approach to improve the performance of XML management systems is to discover frequent XML query paRems and cache their results．Since each XML query call be modeled as a tree structore．the problem of discovering frequent query patterns can be reduced to frequent structure mining．However,mining frequem query patterns is much more complex than simple stroctnre mining since we have to consider the semantics of query patterns．In this paper,we present an approach to discover frequent XML query patterns efficiently．Compared with previous works，onr approach is strictly based on the semantics of XML queries，its mining results arc more precise，and Call be more effectively utilized by caching systerm.