AbstractWith the increase in the main spans of cable-stayed bridges, the wind-induced vibration, especially the high-mode vortex-induced vibration (VIV) of the long stay cables has become a concern for many researchers. In this study, to investigate the high-mode VIVs of stay cables via wind tunnel tests, the mode order amplification factor (MOAF) of the stay cable was proposed to design the flexible stay cable model with a relatively large-scale ratio (λRe) of the Reynolds number (Re). Furthermore, the wind-induced vibration characteristics of the flexible stay cable model with a smooth surface for wind yaw angle (β) of 0° were investigated. In addition, the β effects on the wind-induced vibration characteristics of the stay cable were studied. Finally, double-helical fillets were applied to suppress the high-mode VIV responses of the flexible stay cable model for different β. The results showed that the flexible stay cable model that was designed by the proposed method of MOAF satisfied the similarity of the prototype stay cable and the damping ratios (ξ) of the first several modes of the flexible stay cable model were from approximately 0.021% to 0.064%. The stay cable exhibited five in-plane VIVs in the test wind velocity (V) range for β = 0°. Furthermore, the maximum amplitude of the displacement of the in-plane VIV of the flexible stay cable model decreased with the increase in the VIV mode order. The significant in-plane VIV responses of the stay cable were observed for β of 15°, 30°, −15°, −30°, and −45°, respectively, and the in-plane vibration acceleration responses were significantly larger than the out-of-plane vibration acceleration responses of the flexible stay cable model. The VIV responses of the stay cable could be effectively suppressed through the double-helical fillets with a diameter (d) of d = 0.10 D (where D = diameter of the stay cable) and pitch (P) of P = 12 D.