The impacts of internal and external ice melting factors on ice load are analyzed according to heat balance equation of ice surface, and then the landform factor and the increased equivalent radius of iced line are taken into account for ice load and wind load calculation. The measured meteorological data such as rainfall, wind speed, wind direction, temperature, the power grid operation information, and the monitoring ice thickness information are used to establish the icing-thickness growth forecasting model of transmission line. The framework of icing fault probability calculation is formed via the icing overload mechanism of transmission line. The combined influence of icing-thickness and wind speed on transmission lines is analyzed from the standpoint of mechanics, and the fault probability of transmission line is achieved using exponential model that reflects metal bearing limit characteristic. The actual example verifies that the calculated icing fault probability of transmission lines is consistent with the actual fault trend, and the model can fully verify the correlation between icing fault probability and the actual weather condition.