To improve the structure of the twin seat underframe in multiple unit train and lightweight design, FEM is used to analyze this problem. First of all, the 3D geometric model of the existing twin seat underframe is built. And according to the requirements of enterprises and experiment, the finite element model is built and analyzed. Then results of FEA and experiment are compared. According to the comparison, the finite element model that was simplified is effective. On the basis of effective finite element model, five schemes of the twin seat underframe are proposed and structural strength of twin seat underframes that were improved is researched. Finally according to influence on manufacturing procedure of the twin seat underframe and the error of the FEA, the ideal solution is proposed.