Abstract: Most of the commercial CAD software output the feature based product model in the form of a static description of feature lists，while the relationships among features are always overlooked．Actually，when features are being assembled into a part，they must follow certain definite rules．Based on the classification of features，the space relationships among basic form features and the rules of feature-assembly are studied in the paper．A dynamic，hierarchical feature-based product model，which is built up on the basic of form feature relationship matrix and non-looped graph is presented．The main issues relating to the conversion of a CAD directed model into the hierarchical model in an integrated system，such as： identifying the relationship among features，establishing the relationship matrix and non-looped directed graph，and the algorithm of constructing the hierarchical model are discussed in detail．While a speed regulator box as an instance is given for check．