Current society is trying to realize carbon neutrality according to environmental destruction issues, and inparticular, the automobile market is facing a transition period to eco-friendly vehicles such as electric vehiclesand hydrogen fuel vehicles in order to respond to fuel economy and exhaust gas regulations. In particular,many finished car companies are planning to end the release of internal combustion engine vehicles andpredict the transition to electric vehicles. The transition to eco-friendly vehicles is accelerating R&D on futurevehicles by providing a basic environment for future vehicles such as self-driving vehicles and connectedvehicles. This development causes the weight of the vehicle to increase due to the fusion of various sensors,batteries, control devices, etc., which causes a decrease in fuel efficiency. In order to solve this problem,research on weight car body parts is being conducted. Therefore, in this study, an optimal design study forweight reduction of the front and center floor parts of the car body was conducted by using ultra-highstrength materials and lightweight materials in combination. Optimum design was carried out through finiteelement analysis, and AL6061 was used for light weight material and SGAFC1180 for high strength material,ensuring equal stiffness compared to existing steel and reducing weight by 20%.