The power generation of single-axis PV trackers system is significantly higher than that of the fixed photovoltaic system, so they have been widely used in recent years. The Single-axis PV tracker is prone to torsional aerodynamic instability under a strong wind because of its low torsional stiffness, resulting in structural damage. In order to further understand the occurrence conditions and mechanism of this vibration, the present study investigates the influence of structural natural frequency, tilt angle, damping ratio and other parameters on torsional aerodynamic instability in the wind tunnel tests with elastic support. The variations of aerodynamic damping and aerodynamic stiffness with wind speed and tilt angle are focused. The result shows Torsional aerodynamic instability of single-axis PV trackers shows strong aerodynamic coupling effect, The aerodynamic damping and aerodynamic stiffness are the significant parameters which influence the aerodynamic instability, and sensitive to wind speed and tilt angle，Having some characteristics of self-excited vibration. The increase of torsional stiffness can effectively limit the amplitude at certain tilt angles, and can also improve the critical wind speed of the structure at various tilt angles. The instable tilt angle is approximately in -15° – 20°. It is suggested that large tilt angle can be used to avoid aerodynamic instability under strong wind. When small tilt angle is inevitable. Higher critical wind speed corresponding to 0° tilt angle。