The fretting between wires of transmission lines caused by long-term wind-induced vibration results in rupture of wires easily. The impact of strong wind and rain loads exacerbates the risk, which results in a significant increase in broken strand and broken lines. It’s necessary to study reliability modeling of transmission lines which bears long-term fretting under the impact of strong wind and rain loads. According to theoretical models of fretting, the time-varying structural strength model of aluminium conductor steel reinforced (ACSR) is built up, the contact stress between wires is solved. Thereby the time-varying model of structural resistance is built up. According to the joint action of fretting and strong wind and rain loads, the random nature of transmission line strength and permanent load, the time-dependent reliability model of transmission lines are built up. Numerical results show that fretting degrades reliability model and rain load can’t be neglected under strong wind and rain condition. Time-dependent failure probability model can be used to perfect forecast the rupture risk of wires and make risk warning under inclement weather. The example results prove that fretting will reduce the structural reliability of the transmission line significantly and the strong wind and rain loads increase the risk of the accident.