Wind and rain loads exert a significant influence on the safety of the transmission towerline system. In this paper, the dynamic characteristics of the towerline coupling system in a 110 kV transmission line under wind and rain loads are analyzed. Firstly, the finite element model of a 110 kV transmission towerline system is established in Ansys software, and the modal analysis is carried out. Combined with the theory of Davenport wind speed spectrum and rain load, the windrain coupling load corresponding to the loading node is generated in Matlab. The dynamic response of the towerline system under this coupling load is studied, and the results of its dynamic response under different wind direction angles and with or without rain load are explored. The results show that the grounding wire increases the stiffness of the towerline system as a whole, but because of its strong ‘galloping effect’in the horizontal direction, the coupling effect in the horizontal direction and the alongline direction is different. The wind direction angle of 90 ° is the most unfavorable wind direction angle of the towerline system, and the dynamic response of the towerline system reaches the maximum value. In the case of rainfall of 20 mm/h, the dynamic response range of the towerline system will be increased by about 5 % ~10 % considering the rain load. The effect of rain load on a single tower is almost negligible, which mainly increases the dynamic response of the towerline system by aggravating the galloping effect’of the ground wire.