Most of the input of parametric design system is the specific structure parameter, which is in a detailed design stage. To promote it into conceptual stage, the function-structure mapping problem is proposed. To solve the problem, the function -structure mapping mechanism which is based on logical view and in the framework of axiomatic design is established, the mapping model is solved by optimization method and the mapping procedure is integrated with parametric design system. Function requirements are mapped into a parametric model directly. Finally, a forklift design process validates the method and shows its advantage.