Abstract: Aiming at the vortex-induced vibration problem affecting brides with flat closed-box steel girder caused by ancillary facilities,this paper takes a flat closed-box girder cable-stayed bridge as engineering background,analyzes the vortex-induced vibration performance of the bridge girder through synchronous pressure and vibration measurement tests on a large-scale sectional model,and studies the vibration mechanism and vibration suppression measurements of vertical vortex-induced vibration of this type of section.The test results show that the contribution of the distributed aerodynamic force on the girder surface to the overall vortex-induced force is related to both the pulsation intensity of the air flow on the model surface and the correlation between the distributed aerodynamic force and the overall vortex-induced force.After measurements are taken to suppress vortex-induced vibration,the wind pressure pulsation intensity at each measuring tap on the surface of the girder is significantly reduced,the correlation between the distributed aerodynamic force and the overall vortex-induced force is destroyed,and the contribution of the distributed aerodynamic force to the overall vortex-induced force is reduced.Consequently,the vortex-induced vibration of the girder is effectively mitigated.