As a typical high-rise structure sensitive to wind load，transmission tower has certain risk of collapse in extreme weather such as typhoon. In order to study the wind-induced response of transmission tower and the mechanism of tower collapse，an equivalent scale model of the transmission tower is designed and tested in a wind tunnel. The dynamic response and local deformation of the tower model and its collapse process under strong transverse wind are recorded and analyzed in the wind tunnel test. Further，the structural weaknesses of the model and the change of vertical forces on the bottom main materials are analyzed and compared with the results of finite element method. The results show that the main materials of the transmission tower are susceptible to uneven vertical forces，which increases the probability of metal fatigue under single direction wind load and induces extreme strain in lower middle part of main material of the transmission tower. Therefore，reinforcement of specific parts of main material can effectively enhance the wind resistance of the tower.