Transmission line icing makes serious threats to the safe operation of the power system, to improve the transmission line icing condition assessment accuracy rate, based on transmission line online monitoring system, considering equivalent ice thickness, micro-meteorological parameters and icing duration, transmission line icing condition assessment methods based on support vector machine（svm） and fuzzy expert system is proposed. Support vevtor machine achieved preliminary assessment of the icing status and output lines icing status to determine whether the type of icing exist. Further to make an accurate assessment of the severity of icing using the fuzzy expert system for there is icing and output integrated assessment results of lines icing. Monitoring data of field verified the accuracy and feasibility of the method.