Next-generation high-speed trains are required to achieve higher speeds, enhanced safety, environmental friendliness, and cost-effectiveness. To meet these technical goals, reducing the structural weight to a certain extent is crucial. A standard seat has the following six components: a backrest, a seat cushion, two side and middle armrests, a rear pedal joined with front and rear tables, and a seat bracket. Among these components, the seat bracket, which connects the seat to the carriage, acts as the main load-bearing structure. In the current lightweight design of seat brackets in high-speed trains, the traditional approach is based on structural optimization techniques, often size or shape optimization, with the goal of achieving a desired global stiffness or local stress level, and the optimized structural configuration does not have the best performance under time-varied loads. Thus, it would show a conservative approach, inefficient material utilization, and difficulties in achieving an increasingly stringent lightweight design. On the one hand, the seat bracket’s main structure must have sufficient strength; on the other hand, the key components must not deform substantially under alternating loads because the work conditions under the operation are affected by the track and the application scenarios. Motivated by this, we propose a design and analysis method that integrates SIMP (solid isotropic microstructure with penalization) based topology optimization and direct method (DM) based parameter optimization techniques, where the former applies to the main structure and considers maximizing structural stiffness as a design objective with a prescribed volume fraction constraint and the latter applies to key components, that is, the L-shaped connector, and considers the shakedown limit as the design objective, where the corresponding parametric model is developed and the optimal result is obtained by the genetic algorithm (GA). Using this method, the main load-bearing pathway can be determined and geometric reconstruction design can be performed based on this pathway for the main structure. Compared with the original design, a weight reduction of 17% of the optimized assembled seat bracket is achieved for high-speed trains while ensuring that the mechanical performance meets the requirements. For DM-based parameter optimization design, the load-bearing capacity of the shakedown is increased by 7.8%, and structural efficiency is improved by 23%, with a 12.5% reduction in the material of the L-shaped connector. This study may provide valuable guidance for the lightweight design of similar structures under repeated variable loadings.