Abstract: In the process of product design for national patterns,designers tend to ignore the complex se-mantics implied by ethnic patterns,which leads to the design of products separated from the original cultural connotation of patterns.In view of this problem,the method of product design based on extension semantics of national pattern primitives is proposed.By using the extension theory to extract,quantitatively analyse and illustrate the semantics of ethnic pattern primitives,the application of national pattern in the product de-sign process is optimized.Taking the brocade of Dong nationality as an example,firstly,the pattern primi-tives of Dong brocade are extracted and selected by the local culture holders and designers.Secondly,the extension semantics of pattern primitives is analyzed,and the characteristic words of the maximum exten-sion design interval are obtained.Thirdly,the characteristic words are illustrated,and the illustration with the maximum extension design interval is analyzed.Fourthly,the illustration is analyzed to guide the design practice.Finally,the designer and the local culture holders are invited to jointly evaluate the cultural expres-sion,innovation and beauty of the design scheme,select the design scheme with higher quality,design and produce the specific product,all of which improves the accuracy and superiority of the use of national pat-terns in the process of product design.