Abstract: Scheme design is the key stage of product design process.To reuse the design knowledge and the design experience implicated in the existing design,a method of extension association rule mining and reuse was proposed.This method introduced extension theory;the design knowledge was formally described with basic element;the basic element implication model of product design process was established based on its implication;a kind of improved FP-growth algorithm of association rule mining was proposed;extension association rules were mined from product case library;a knowledge reuse model based on extension association rule reasoning was established.Finally,the feasibility and efficiency of the method were verified by an example of hydraulic turbine scheme design.