A nonlinear finite element method was used to investigate the derailments of trains moving on multispan simply supported bridges due to damage to suspension systems. At the simulation beginning, the initial vertical trainloads to simulate the train gravity weight are gradually added into the mass center of each rigid body in the train model with large system damping, so the initial fake vibration is well reduced. A suspension is then set to damage within the damage interval time, while the spring and/or damper changes from no damage to a given percentage of damage. Finite element parametric studies indicate the following: (1) the derailment coefficients of the wheel axis nearby the damage location are significantly increased. (2) Damage to the spring is more critical than that to the damper for the train derailment effect. (3) The derailment coefficient induced by damage to the primary suspension is more serious than that to the secondary suspension. (4) If rail irregularities are neglected, the train speed has little influence on the derailment coefficients generated from damage to suspensions. (5) The train derailment coefficients rise with a decrease in the damage interval time, so sudden damages to suspension systems should be avoided.