Insulator flashover caused by atmospheric icing is a serious accident with high frequency. The flashover risk on insulators during ice-melting process is higher than that during icing accretion process. Therefore, it is of great theoretical significances and engineering value to carry out research on risk prediction methods of ice-melting flashover on insulators. Firstly, this paper presents a thermal balance equation of the iced insulator surface for icing natural melting process and calculates the main influencing parameters of the ice-melting process by thermodynamic analysis. Secondly, this paper extracts the meteorological data from great numbers of on-site ice-melting flashover cases to calculate the meteorological condition with the highest flashover risk. On the basis of this, to judge the state of freezing or melting, a thermodynamic criterion of freezing and melting state is proposed, and the finite element analysis is applied to model iced and non-iced insulators, and the temperature distribution, the wall heat transfer coefficient distribution of the airflow field are analyzed. The results suggest that the local micrometeorological temperature and the heat transfer coefficient have the greatest impact on the ice-melting process of insulators. The structure of insulator will be changed by the covered ice, ended up to a cone-like structure which will weaken the influence of the vortex on the central leeward side. The heat dissipation and melt characteristics of iced insulator will be quite different from that of non-iced insulator.