Abstract: Icing disasters seriously affect power system. The accurate measurement of transmission line's equivalent icing thickness is of important significance for preventing icing disaster. Conductor's sag is a notable index which can be used to telemeter the ice-thickness of conductors after icing. Therefore, based on the analysis of conductor's mechanical properties, with the measurement of conductor's sag and surface temperature, a computational model of equivalent icing thickness on transmission line under complex load was built. Moreover, different types of conductors under continuous spans and high elevation discrepancy span with uneven distribution icing were taken as objects, and the monitoring process and parameter calculation under standard condition were carried out in this research. To verify the proposed method, a natural icing test of conductor was carried out at the Xuefeng-mountain Natural Icing Test Base of Chongqing University. The experimental results show that the computational model has high accuracy in icing monitoring, and the maximum error of equivalent icing thickness is 11.1%. For a certain conductor, the maximum sag f_M varies approximately linearly with the equivalent icing thickness. Under a certain monitoring accuracy, the requirement of f_M's measurement accuracy increases exponentially with the increase of conductor geometry. When the span is above 400 m, the temperature measurement only needs to achieve ±1 ℃, and the sag measurement accuracy achieves ±1 dm, then the measurement accuracy of equivalent icing thickness growth can achieve 1 mm.