The detail design for overhead line can be divided into a MD(Mounting Diagram) design and pegging plan process. A MD design for a high-speed overhead line was performed by the design software. The MD design of Honam High-Speed catenary system was also performed the software. However, the MD design software for 400km/h overhead line is needed, because the tension of wires and conditions are different from 350km/h system. Therefore, in this study, a MD design software for 400km/h overhead line system is developed.