Abstract: A composite web service can be constructed by combining together the component services which have different non-functional QoS (quality of service) attributes. A problem is thus caused, i.e., how to select the most suitable services in accordance to the different QoS attributes as criteria as to meet the global QoS requirements of the composite web services. To solve the problem, an approach is proposed to simply the complex process model of the composite service with the layered graph technique used to reduce the problem to be a routing problem in directed graph. Then, the selection algorithm for the composite service is performed taking no account of different flow operations, such as sequence, selection, concurrency and loop, thus reducing the complexity of selection algorithm and improving execution efficiency. According to the simplified model and based on adaptive genetic algorithm, a QoS-aware selection algorithm is given for composite web services. Simulation results showed that the proposed approach is feasible and effective.