Abstract: A policy-desire-contract extended agent model （PDC-Agent） is proposed to establish automatic composition of web services.According to the three types of factors such as policies,desires and contracts,PDC-Agent rationally select the intended services and their properties by virtue of a preference-based decision-making mechanism, and participate in virtual-organization （ VO ） formation and service composition.The process of autonomic service composition and a case study are presented.This system can well adapt to the variation of business requirements and perform real-time application integration in the open,dynamic and heterogeneous VO environment.