Temporal description logic ALC-LTL not only has considerable expressive power, but also extends the description capability of description logic from the static domain to the dynamic domain. In this paper, ALC-LTL is applied for the composition of semantic Web services. We take the view that atomic process and composite process in the OWL-S ontology can be considered as atomic service and composited service respectively. Inputs, outputs, local variables, preconditions and results of atomic processes can all be described with ALC-LTL. Based on the models of services, the executability problem and the projection problem of Web services can be reasoned about effectively.