 This paper evaluates the safety performance of a hydrogen fuel cell city bus body frame through finite element analysis under four typical operating conditions. The simulation results show that the body frame meets stiffness design requirements but exceeds material yield strength and fails to satisfy strength design requirements under emergency cornering and ultimate torsion conditions. A size optimization method is employed to reduce maximum stresses by up to 20.13% meeting strength design requirements and achieving a weight reduction of 106 kg. This article was authored by Rong Yang, Wei Zhang, Xu Yuli, and others.