Abstract: In order to study the accumulative damage evolution law of fatigue for viaducts under impact dynamic response of trains, the 32-meter prestressed-concrete box girder of the Beijing-Tianjin Intercity High-Speed Railway was taken as a prototype to design and manufacture three scale-model beams. A multi-stage variable-amplitude fatigue-loading test was performed on the model beam. The design and fabrication of scale-model beams and the loading and acquisition process of multi-stage variable-amplitude fatigue-loading test were introduced. The development of crack and sensitive damage locations of box girders under fatigue load, as well as fatigue evolution laws and generation mechanism of deflection, rebar and concrete strain were studied. It was concluded that the fatigue of box griders should pay more attention to web parts; the larger the fatigue amplitude, the larger the mechanical indicators such as deflection, rebars and concrete strain, and the more serious the accumulative damage of griders.