A product family extension configuration method based on evaluation model for customer demands, relational mapping and extension association rules is introduced to better realize rapid and effective product configuration. A demand-based evaluation model is confirmed by the information of customer demands and a mapping relationship between demand-based model and characters of product family cases is built. The similarity between evaluation model and product family cases is up to the association rules and a product family case with the highest similarity can be extracted according to association rules. According to the situation of the similarity, the extracted case is modified to meet the demands of configuration with case-based reasoning method. The method is validated by a speed reducer case.