Windinduced dynamic behavior of a highvoltage transmission towerline system is investigated through an aeroelastic model test in a boundary layer wind tunnel.Dynamic tower failure phenomena were reproduced in wind tunnel tests for the first time.Test results show that the windinduced vibration of the towerline coupling system is of a distinctive nonlinear characteristic. The higher the wind velocity is, the more distinctive the nonlinearity is. Chaos arises in the vibration of the tower structure as the wind velocity reaches certain value. The higherorder model vibration of the towerline coupling system is remarkable and the energy of it is even stronger than that of the lowerorder model.The influence of the wires and insulators to the wind responses of the tower enhances as the wind speed increases.The higherorder model vibrations should be considered when the windinduced dynamic responses of the transmission tower are analyzed.The nonlinear vibration of the wires and insulators should also be considered while designing a transmission tower.