Abstract: There are three subspaces of product design state space, namely function (F), behavior (B) and structure (S), the mapping among them form the evolutionary process of design. In this paper, we focus on the mapping between function and behavior, modeling the relationship between function and behavior by fuzzy theory, but the coupling of relationship between these two spaces presents a barrier, therefore, we introduce an orthotropic model for releasing the coupling, and construct common integrated variables of behavior. From these variables, the character of these behaviors can be extracted, so the way of mapping between two spaces will be revealed. Finally, a multi-functional experimental bench for certain mechatronic products is taken to verify the approach.