Abstract: Objectives In this study, the lightweight design method and optimal design scheme of vehicle deck structure are proposed for the special vehicle load characteristics and its most hazardous working conditions loaded on a ro-ro ship. Methods Firstly, the hazardous working conditions of the vehicle deck under special vehicle loads were obtained by direct finite element calculation and parametric modeling; Secondly, based on the mixed-integer sequence quadratic programming algorithm, a lightweight design method for vehicle deck structure satisfying local strength is proposed; Finally, for the most dangerous loading condition of a ro-ro ship, the optimal design scheme of vehicle deck structure is obtained. Results The proposed optimized design scheme reduces weight by 25.88% compared with the initial scheme; the number of fatigue life cycles of the vehicle deck is 80537, and the local strength stability and fatigue strength meet the specification requirements. Conclusions The study shows that the reasonable arrangement of vehicles can significantly reduce the structural stress level; optimization of deck plate thickness is the most effective solution to reduce the weight of the vehicle deck. The proposed lightweight design method can provide a reference for the optimized design of a vehicle deck of the same type of ro-ro ship.