Under the action of external environmental forces, transmission lines are prone to accidents such as fatigue damage and fracture of connecting fittings caused by excessive load bearing. The existing research focuses on the influence of ice accumulation and strong wind load on connecting fittings. However, the mechanism of action and influence mechanism of low-frequency resonance of transmission lines caused by breeze environment on the load bearing of connecting fittings are still unclear. The Karman vortex street effect and periodic lift force of the conductors caused by aeolian vibration were analyzed. With the suspension insulator string as the research object, a three-dimensional simulation model of the 220 kV tower line system and the suspension insulator string was established to explore the mechanical response characteristics of the suspension insulator string under the resonance of the transmission lines in the breeze environment. The simulation results show that the resonance of the transmission line in the breeze environment would significantly increase the stress level of the suspension insulator string. The stress concentration position of the suspension insulator string under the resonance of the transmission line is at the ball-rod joint of the ball eye, and the maximum equivalent stress is 548.4 MPa. The research results indicated that the resonance of the transmission line in the breeze environment would have a significant impact on the connecting fittings, providing a basis for the structural optimization design of the connecting fittings and the operation and maintenance of the key areas of the transmission lines.