A novel overhead transmission line icing thickness measurement method based on transmission traveling wave time difference is proposed. Theoretical derivation of the relationship between icing thickness and transmission line length is presented. The traveling time of the traveling wave caused by external fault and operation is recorded by GPS traveling wave fault location system. Transmission line length changes are measured， then the icing thickness can be calculated. The actual operating data of a regional power grid during the 2008 ice disaster shows that the method has applicability and can be adapted to analysis the ice disaster and provide reference for deicing arrangements.