The invention discloses a device for reducing power transmission line clamp corona discharge. The device comprises a metal mask and a locking device. The metal mask comprises a rectangular top face and four side faces, and the edges are in smooth circular bead transition; the locking device comprises a slip sheet and a spring, and the slip sheet is movably installed on the rectangular top face; athrough hole through which a bolt on a power transmission line clamp runs is formed in the rectangular top face, and the through hole is formed in the moving path of the slip sheet; the spring is fixedly connected to the slip sheet so that force enabling the slip sheet to move towards the through hole can be applied to the slip sheet. The device for reducing power transmission line clamp corona discharge solves the technical problem that in the prior art, corona discharge is generated due to the fact act the curvature radius is excessively small at a high-voltage power transmission line clamp.