The invention discloses a power transmission line icing state early warning method, device and system, and relates to the technical field of power monitoring. The method is based on optical measurement of a distributed icing state carried out by a distributed icing on-line monitoring device along a sensing carrier of a current power transmission line. The method includes the following steps: S1, analyzing key risk factors according to parameters of a trend early warning model, and carrying out icing trend early warning on an icing condition of the current power transmission line; and S2, carrying out icing real-time early warning on the icing condition of the current power transmission line according to a real-time early warning mechanism and an icing ratio calculated based on the key riskfactors. The power transmission line icing state early warning method, device and system of the embodiments of the invention can realize high-accuracy early warning on the icing condition of the current power transmission line, can discover potential danger of the line in time and reflect the perspectiveness of the icing early warning.