In this paper, product structure is taken as knowledge acquisition point, and the effective knowledge acquisition path is discussed by establishing the associated relationship between design demands of different design stages and corresponding product structure. The establishing method is to integrate rough set and artificial neural network (ANN). Design demands are reduced so as to form effective decision conditions by applying rough set. ANN model between design demands of different design stages and corresponding product structure is established to determine product structural style quickly by applying ANN, so that the needed design knowledge is acquired during design process. Finally, the general schematic design process of a roll plate machine is taken as the example to discuss the fusion application of rough set and ANN, and certify the effectivity of this method.