The transmission line is easy to ice severely in winter because of the influence of terrain climate in southern mountain area, which brings great challenge to the safe operation of power system. Therefore, it is important to discover the law and to find the defect of the icing data in this area through researching transmission line icing. Firstly, the principle of on-line monitoring system for transmission line icing is discussed. On this basis, the characteristic of icing is analyzed based on the on-line monitoring data. Moreover, the law of the influence on the ice of the combination of various meteorological parameters is summarized in different micro meteorological conditions of this mountain area. Finally, a method based on fuzzy logic and artificial neural network is proposed to build the combination model for forecasting the icing of the transmission line.