Due to the excellent mechanical and economic performances of the Π-shaped steel-concrete compos? ite girder, it is widely used in long-span cable-stayed bridges. However, the aerodynamics performance of the girder is relatively poor, and the vortex-induced vibration (VIV) of the girder is prone to occur for the improper aerodynamic design, which affects driving comfort and safety, or structural fatigue. Based on Chao-Shan Bridge in Guangdong, a single-pylon cable-stayed bridge with a main span of 205 m and Π-shaped steel-concrete composite deck, the in? vestigations on the VIV and aerodynamic countermeasures of the Π-shaped steel-concrete composite deck were con? ducted. Firstly, the VIV of the original girder section in-service state was studied by applying wind tunnel tests of the rigid segment model with a length scale of 1∶50. Then, the effects of aerodynamic countermeasures on the VIV of the Π-shaped steel-concrete composite girder, such as the lower stability plate, the deflectors, the skirt plates, and the upper central stability plate were studied, respectively. Finally, the computational fluid dynamics (CFD) method was adopted to study the control mechanism of the aerodynamic countermeasures. The results show that there is a large vortex vibration of the original girder section within the design wind speed, and the peak value of the VIV exceeds the limit value of the specification. The VIV of the girder can be controlled remarkably with the combined countermea? sures of three lower stability plates, vertical skirt plates on both sides of the girder, and an upper central stability plate. The control mechanism of the combined countermeasures on the VIV of the Π-shaped steel-concrete compos? ite deck is mainly as follow: the three lower stability plates can effectively destroy the large vortexes on the lower side of the girder; the vertical skirt plates set on both sides of the girder can improve the aerodynamic streamline of the girder and the upper central stability plate can effectively prevent the movement of the larger vortexes on the top side of the girder.