The invention discloses a deicing device and method of a high voltage transmission line. The deciding device comprises a first fixing sleeve and a cleaning blade, the first fixing sleeve is mutually connected with a first roller via connecting pieces at left and right sides, the first fixing sleeve is positioned over a cable, the first fixing sleeve is mutually connected with a second fixing sleeve via an adjusting bolt installed in the outer side, a drainage groove is formed in the second fixing sleeve, a connecting shaft is installed under a driving motor, a breaking cutter is arranged outside the connecting shaft, cutting teeth are arranged at one side of the breaking cutter, and the second fixing sleeve is mutually connected with a second roller via connecting pieces in front and backsides. According to the deicing device of the high voltage transmission line, the first and second fixing sleeves can be dismounted, installation is convenient, the walking motor drives the first roller to walk, the breaking cutter cuts and breaks falling icicles before deicing by the cleaning blade, and thus, the deicing efficiency is improved.