Based on the vehicle-bridge coupling vibration theory and the field test of ground-based microwave radar, the stress impact coefficient of suspender of high-speed railway arch bridge is studied. The train and track-bridge are modeled by multi-rigid-body dynamics and finite element method, respectively, and the train-track-bridge coupled system model is established based on the equivalent Hertz linear wheel/rail contact model. The displacements of the top and bottom of the suspenders are tested simultaneously by the ground-based microwave radar system. The dynamic characteristics of the bridge, the time-history of stress and the stress impact factor of suspenders are obtained. The experimental data of ground-based microwave radar are compared to verify the correctness of the theoretical model. Based on the model, the influences of driving speed, single or double line driving and track irregularity on the stress impact factor of the suspenders are analyzed. The results show that the stress impact factor of suspender increases with the increase of vehicle speed. When the speed is 300km/h, the stress impact factor of the suspender increases significantly due to the resonance of the axle. Due to the low static stress of suspender caused by train load, the impact factor of suspenders during single-line driving is larger than that of the double line. The German low-interference orbit spectrum sample has little effect on the stress-impact coefficient of the suspenders, but the stress impact factor increases significantly with the deterioration of track smoothness.