The work aims to propose a product design method based on extension semantics and shape grammar to solve the uncertainty of shape-meaning matching of cultural resources of Yi sun patterns in the process of design transformation. With the sun pattern on Yi lacquerware as an object of study, its cultural factors were analyzed and the characteristic vocabulary was extracted to construct a topographically representable model, which was used to quantify the relationship between patterns and cultural semantics. Then, the cultural connotations and values were evaluated by calculating the toposable space of its semantics, and the semantic mapping of words was conducted to obtain superiority representations and core semantics. With the graphical interpretation of lexical semantics, the superiority representation and core semantics of sun pattern could be obtained. According to the method of shape grammar, the sun pattern was deduced by setting the optimal graphical semantic as a constraint, and its original shape, color and iconographic features were combined to generate the innovative patterns. Finally, based on the graphical semantics, the comprehensive assessment of new pattern and its verification of form-meaning suitability were performed. Extension semantics and shape grammar are effective in the innovative design of the Yi sun pattern, providing a reference path for the inheritance and development of Yi sun pattern culture.