Based on the Linyi Yellow River Bridge in Shanxi Province, experiments and computational fluid dynamics (CFD) numerical simulations were conducted to study the mechanism of vortex induced vibration (VIV) and aerodynamic countermeasures (AC) for a steel box- concrete composite girder with sound barriers. Firstly, wind tunnel tests were conducted on the original design scheme of the girder section using a segment model with a geometric scale ratio of 1:60. Then, experimental studies were conducted to investigate the influence of the installation position of horizontal guide plates on the VIV control performance, including installing 2.0 m-wide horizontal guide plates on both webs of the steel box–concrete composite girder at a height of 2.6 m above the bottom plate (AC-1), as well as installing 2.0 m-wide horizontal guide plates at the ends of the flange plates (AC-2) . Finally, CFD simulations were performed to analyze the vortex-induced vibration and control mechanism of the original design scheme of the steel box-concrete composite girder section with/without AC-1 and AC-2, respectively, based on flow field characteristics. The results show that the original design scheme of the steel box-concrete girder section exhibits both vertical and torsional VIV at 0 ° and+3 ° angles of attack, and the maximum amplitude exceeds code-specified limits. After adopting the aerodynamic control measure AC-1 on both sides of the steel box-concrete composite girder at a height of 2.6 m above the bottom plate, the torsional VIV response of the girder section is eliminated, while the vertical VIV amplitude slightly increases. Furthermore, after adopting the aerodynamic control measure AC-2, the VIV amplitude of the girder section was effectively suppressed, and the torsional VIV of the girder disappeared. Moreover, the mechanism of VIV and aerodynamic control of the steel box-concrete girder section with sound barriers can be summarized as follows: the airflow passing over the girder section induces alternately shedding vortices on the downstream side, which leads to vortex-induced vibration. The vortex intensity shows no significant reduction after adopting the aerodynamic control measure AC-1, while the vortex intensity is weakened to to a certain extent after adopting the aerodynamic control measure AC-2, whichc ontributes to the effective suppression of the VIV response of the girder section.