The invention relates to a sag trimmer of a split conductor of an overhead power transmission line. The trimmer comprises a transverse rod and a threaded rod, wherein the transverse rod is perpendicular to the split conductor and is fixedly connected with a line tackle sheave groove arranged on the split conductor; moreover, the transverse rod is provided with adjusting holes and the positions of the adjusting holes are in one-to-one correspondence with each split conductor; the threaded rod passes through the adjusting holes; one end of the threaded rod passing through the adjusting hole is provided with a nut, while the other end is provided with a holding clamp; and the holding clamp is sleeved on the split conductor. The sag trimmer of the split conductor of an overhead power transmission line provided by the invention has simple operation, convenient overhead operation and high adjusting efficiency and can adjust the sag of a single subconductor.