In design processes of machinery, much computer software, for examples CAD/CAE/CAM software, are used. The design processes are aided by this software. The seamless connections of the design processes are necessary for the improvement of the cost benefit of the products. However, sometimes, the conflicts among designs or design processes are occurred by the change of the design at a certain design process and these conflicts are should be noticed and solved immediately. In this research, we have developed the design system including CAD software and the developed system has some functions to find the conflicts of the change of designs and to solve the conflicts. We use Data Envelopment Analysis (DEA) to calculate the efficiency of the design and Satisficing Trade-off Method (STM) to find and solve the conflicts. We have confirmed through some fundamental numerical examples and discussed of the proposed system and method and showed the effectiveness of out study.