Aiming at aerodynamic performance of a long-span cable-stayed bridge stiffened with π-type composite girder, a rigid segment model was used to conduct systematic wind tunnel tests for the bridge completion state. Test results showed that the bridge main girder has obvious bending-torsion coupled vortex induced resonance within the range of designed wind speeds, even damping ratios of both vertical bending and torsion directions are increased to reach 1%, there is an obvious vortex induced resonance phenomenon and its amplitude exceeds the specification limit. Spectral analysis showed that the bridge main girder’s vertical bending natural frequency is consistent to its bending-torsion coupled vortex induced resonance frequency, the main girder’s vortex vibration “lock-in” frequency is close to its vertical bending natural frequency. The frequency characteristics and causes of bending-torsion coupled resonance of the main girder section were discussed and analyzed. Through wind tunnel tests, a series of aerodynamic vibration reduction measures including central stabilizer plate, side stabilizer plate and guide plate were studied from the point of view of parameterization, and the optimal vibration reduction scheme was proposed to effectively suppress the bridge’s vortex induced resonance phenomenon. The study results provided a reference for the design of vortex induced resonance vibration reduction of similar bridge sections.