Abstract: Localized severe wind such as downbursts is responsible for structural failures of transmission lines because it is always characterized by small size, high intensity and sudden change. The purpose of the study is to search a theoretical analysis framework for investigation of the dynamic response of transmission towers under downburst attack in frequency domains. To begin, using the theoretical model for time-varying mean wind and for non-stationary fluctuating wind, the expressions of impacting wind load on a transmission tower by the moving downburst in time and frequency domain are developed respectively. Upon the random vibration theory, the frequency domain solution of non-stationary fluctuating wind-induced response of transmission towers is proposed. Subsequently, through the extreme value theory of first-passage, the extreme value probability distribution of dynamic response under the non-stationary downburst wind load was proposed in theoretical approach , as well as the simplified solution for peak factor by equivalent stationary extreme value distribution are supplied. The accuracy of the frequency-domain theoretical method was verified using the finite element transient dynamic analysis results of random samples. This study indicated that the multi-source non-stationary excitation at different heights of the tower can be simplified to synchronous slow-varying excitation. The theoretical solution of non-stationary response extremum distribution has high accuracy, and the peak factor by equivalent stationary extreme value distribution is convenient and slightly conservative. The study provides a theoretical basis and technique for the improvement of thunderstorm-resistant design of transmission towers.