Current QoS-aware automatic service composition queries over a network of Web services are often one-time innature. After a network of Web services is built, such queries are issued once, and answers are found from the scratch. The underlying assumption is that the participating Web services are rather static so that their functional and non-functional parameters seldom change. However, such an assumption is often baseless. New services come and go, service APIs change gradually, and QoS values fluctuate. Therefore, a support for efficiently handling "continuous" service composition queries is desired. In this paper, we propose an event driven continuous query algorithm for QoS-aware automatic service composition problem to cope with different types of dynamic services. Moreover, we integrated this algorithm in our service composition system, QSynth. Finally, we evaluate our proposal using both real QoS data and synthetic Web service data and show the superior performance of ours, compared to the state-of-the art solution which won the performance championship of Web Service Challenge in 2009 and 2010.