The Π-shaped composite girder is widely used in the construction of long-span cable-stayed bridges， but the weak vortexinduced vibration （VIV） performance of this type of section seriously limits its application prospects. A Π-shaped composite girder double-tower cable-stayed bridge with a main span of 530 m is used as the engineering background， and the VIV performance and aerodynamic optimization measures of the Π-shaped composite girder are studied by using wind tunnel tests. The tests show that the VIV of the original Π-shaped section occurs at each wind attack angle， and the VIV amplitude of the girder can be reduced by setting guide vanes and the lower central stabilizer. The change in the inclination angle of guide vanes has a significant impact on the combined aerodynamic measure of VIV suppression performance. The combination measure VIV suppression performance with the guide vane of 30° inclination angle is the best， and the VIV can be significantly suppressed or even eliminated when the damp? ing ratio required by the specification is 1.0%. The VIV suppression mechanism of the combined aerodynamic measure and the in? fluence mechanism of the guide vane inclination angle change on the VIV suppression performance of the measure are studied by us? ing computational fluid dynamics （CFD） numerical simulation. The calculation results show that the windward side guide vane in the 30° inclination guide vane combination measure can significantly improve the gas flow around the upstream section， and the co? operation with the lower central stabilizer can weaken the Karman vortex of the Π -shaped section wake toy suppress the girder VIV. Changing the inclination angle of the guide vane not only affects the generation of vortices near the guide vane itself， but also affects the improvement of the lower central stabilizer on the vortex shedding state under the section， thereby significantly affecting the VIV suppression performance of the combined aerodynamic measure.