Abstract: Studies have shown that the facade appurtenances of high-rise buildings, such as horizontal and vertical ribs, can significantly reduce the wind load acting on buildings. However, the working mechanism of these aerodynamic optimization measures remains unaddressed. The most effective method to solve this problem is to compare and analyze the flow field around the building before and after aerodynamic optimization to figure out the effect of optimization measures on the flow field. In this paper, the influence of five different rib’s layouts on the flow field around a high-rise building was investigated through the Particle Image Velocimetry (PIV) test. The effect of extensional ribs with different layout on the average and fluctuating flow field was compared, the wind resistance performance of extension ribs was analyzed, and the aerodynamic optimization mechanism of facade appurtenances was figured out. The results show that the horizontal continuous ribs can obviously restrict the vertical flow and reduce the turbulence intensity inside the shear layer. Compared with horizontal ribs, the vertical ribs can more significantly modify the fluctuating flow field around the model. The vertical ribs near the building corner can change the flow separation at the leading edge, and reduce the curvature of the shear layer. Consequently, the turbulent intensity of the along-wind and crosswind around the building is obviously mitigated. The horizontal and vertical ribs significantly increase the size of the wake vortex in the along-wind and crosswind directions. The changes of the above flow field characteristics directly affect the average and fluctuating wind loads acting on the building.