Electro-thermal Coordination (ETC) power flow model can obtain the calculation results of power flow and line temperature at the same time, which can provide a strong support for power network operation analysis and decision-making. However, the current ETC power flow model ignores the randomness of weather conditions on the overhead line and cannot describe the random influence of weather conditions on power flow and line temperature. Therefore, this paper proposes an ETC power flow model which takes into account the meteorological randomness of the line. Firstly, the Markov Chain method is employed to randomly simulate these weather conditions in the model, base on this then the coupling solving of the heat balance equation and the power flow equation is carried out, and finally obtains the statistical law of the power flow distribution and changes of the line temperature. A case study shows that the ETC model can reflect the influence of meteorological randomness on power flow and line temperature, and effectively obtain the risk of line overheating during power network operation.