The anti-yawing damper installed between the carbody and bogie is an important component to improve the hunting motion stability of a railway vehicle. With the increase of service mileage, fatigue cracks occur in the weld joint between the carbody anti-yawing seat and underframe side beam, which seriously threatens the vehicle safety. A finite element simulation, bench test, and on-track test were carried out to analyze the dynamic stress and load of an anti-yawing seat. These studies showed that the longitudinal load induced by the anti-yawing damper is the primary load acted on the seat, which is higher than the design load and causes the weld joint failure.