The product model for conceptual design was built based on function-structure relation. Firstly, the function model was established, in which the meta-function and input/output flow were modeled with the functional basis approach, and the dynamic behavior of input/output flow was described with the language of bond graph. Secondly, the structure model was established based on component-connector relation, in which physical hierarchy was described with undirected graph. Functional features were extracted subsequently, which consist of meta-function, flow object and relational constraints. The design concepts were generated by the decomposition of function and mapping between function and structure. Finally, a design case of transmission system was given to demonstrate the proposed model.