Abstract: For the redesign of existing products, a process-oriented method combining functional structure model and extension theory is proposed. In order to reach the goal, this method is based on the knowledge base of functional ontology, the functional structure of existing products is built, the adverse affairs of products are expressed by affair element model, the causes of adverse affairs are inferred by implication system analysis of extension theory, and the problematic functions in product functional structure can be confirmed by the analysis results. After that, the problematic functional affair element model is created. Based on the reasons of adverse affairs, the extended analysis and extension transformation are carried out to obtain the improved new function, then the new function structureconstructed, and the redesign of the existing products completed. Finally, the feasibility of the method is verified through the redesign of a pineapple picker patent, which provides a new idea and an operable method for the redesign of existing products.