With a typical section of 220 kV four circuit transmission line in West Inner Mongolia, the structural strength and fatigue life of the towers under stochastic wind are numerically studied using the finite element (FE) method. The FE model of the tower-line system is established using the ABAQUS software. Considering the topographic characteristics of the West Inner Mongolia, stochastic wind fields are simulated numerically to calculate the dynamic response of tower-line system. According to dynamic responses of the tower-line system under wind load, the dangerous zone of the tower is determined and its 3D solid FE model is set up. A hybrid FE model combining the local 3D model with the spatial beam model of the other portion of the tower is constructed. The time histories of the reaction forces at hanging points of the conductors and ground wires are applied on the hybrid FE model of the tower to simulate its dynamic responses under wind load. The structural strength and fatigue life of the tower under two stochastic wind fields and with different bolt preloads are numerically investigated. The results show that the bolt looseness obviously affects the strength and fatigue life of the tower and may be one of the main reasons of tower failure.