Workflow is the key technology for business process automation, while distributed workflow is the solution to deal with the decentralized nature of workflow applications and the performance requirements of the whole system. In this paper the architecture of distributed workflow execution is given, and the centralized model called CWF-net, which is based on colored Petri net, is presented. Based on the centralized model, a novel model fragmentation algorithm is proposed. This algorithm partitioned the centralized model into fragments by duplicating the places shared by transitions which are executed in different sites. The behavioral equivalence between the CWF-net and resulted fragments are guaranteed by the extended firing rules. Then the correctness of the fragmentation algorithm is discussed, the correctness criteria comprises completeness of the fragmentation, completeness of each fragment, and the behavioral equivalence after fragmentation. Finally the future research work is poin...