In order to adapt to the inconstancy of business environments and service requirements, a model of dynamic workflow and its rewriting net are defined. Some good properties of the model and its rewriting net such as inheritability, reversibility, transitivity, and soundness are proved. In order to achieve programmable, structural, online and o2ine changes, their corresponding mechanisms are established. The model and mechanisms can be used to analyze and implement dynamic processes and process changes automatically. Process dynamics may depend on both structural and functional changes which constitute the two methods of process change deployment. This paper adopts a DPLW (Dynamic programmable logic workflow) model based on Petri nets to design and implement dynamic business processes. A prototype is given to demonstrate the proposed model and mechanisms to deal with process changes.