The front longitudinal beam (FLB) is the most important energy-absorbing structure of a vehicle in a front crash. Its structure directly determines the safety performance of a car and the effectiveness of passenger protection. The purpose of this paper is to perform the parameter study and cross-section shape optimization of FLB with variable cross-sectional shape (VCS FLB). Firstly, the effect of flanging perimeter ratio and aspect ratio on the deformation behaviors of VCS FLB are studied, and then the reasonable ranges of the cross-sectional shape parameters are obtained. Thirdly, a simplified finite element model of VCS FLB is constructed. Finally, a multi-objective crashworthiness optimization design of VCS FLB is performed by integrating response surface model (RSM) and NSGA-II algorithm. The results demonstrate that the energy absorption, maximum peak force and deformation patterns are superior to their initial counterparts, and that cross-sectional shape optimization can improve the crashworthiness performance of VCS FLB significantly.