Abstract: An attempt is made to express assembly semantics in terms of a set of symbols and establish a new scheme for representing assembly model. The expression, transformation and maintenance of design semantics are presented, which enable the designer to specify detailed assembly relations via abstract semantics. In addition, description of set of rules using assembly symbol is proposed to transfer the product assembly design information, and assembly symbol relation graph (ASRG) is used to dynamically maintain the assembly semantics and constraints. Through the transformation of design semantics, the abstract, fuzzy and dynamicly associated information are processed by the product assembly design system to generate concrete, precise information of product assembly.