Forming Process Design needs simultaneous consideration of multiple factors, accuracy of products, costs and cycle time. Consequently, its design knowledge is based on personal experience and tends to be implicit and untransferable in general. To represent and transfer such implicit and personal design knowledge of forming process, we propose a novel knowledge mining method based on graph theory. Experienced engineers’ knowledge is transcribed as a set of statements through a series of interviews. Then, the interrelationship among these statements is clarified by translating them to a graph-based knowledge representation model. Implicit knowledge is extracted as structural characteristics of the graph.