The invention provides a construction method and device for a power transmission line tower system aeroelastic model. The method comprises the following steps that: firstly, obtaining the environment parameter information of a power transmission line tower system to construct a wind field model; secondly, obtaining power transmission line tower structure information and historical weather information, and determining a quantitative function relationship between windage yaw flashover and the power transmission line tower structure information under the wind field model; thirdly, according to the function relationship, establishing a multiphase coupling mathematical model; and finally, carrying out numerical calculation on the multiphase coupling mathematical model to establish the power transmission line tower system aeroelastic model. In the method, a computational fluid dynamics method is adopted to carry out numerical simulation on the multiphase coupling flow field of the power transmission line tower system. Compared with the prior art, the established aeroelastic model can assist in analyzing the wind-induced damage mechanism of a high-voltage power transmission line tower system, and therefore, the problem that a traditional model construction method does not conform to the characteristics of microtopography and microclimate environment.