Abstract: Fuzzy mathematics model built up on the basis of polychromatic sets is developed to modeling and analyzing the discrete system．Design rules and search algorithm are worked out for conceptual design of mechanical products．The search algorithm is able to find out several feasible schemes of product design conforming to the established technical specifications，resulting in a set of candidate solutions．Evaluation functions are applied to choose the most reasonable one．An example of machining center layout is presented to illustrate the feasibility of new approach．