The invention discloses a method for grounding a single-core high-voltage cable metal sheath, which comprises the following steps: the cable metal sheath is led to the line inlet end of a grounding box by a coaxial cable; then the grounding end of the grounding box is connected with a grounding belt by a grounding wire; a parallel connection grounding line is also arranged between the grounding box and the grounding belt; one end of the parallel connection grounding line is connected with the original grounding line by a grounding wire clamp, and the other end is connected with the grounding belt by a grounding bolt; and both the grounding wire clamp and the grounding bolt are carried out seal processing by a waterproof adhesive tape. The invention effectively solves the problems of leakage current increase, grounding point heating and power failure overhauling processing on a high-voltage cable, which are caused by grounding point resistance increase because of oxidation and corrosiondue to the damp of the grounding end of the cable line metal sheath erected on a channel, and can be widely applied to the running and the overhauling maintenance of a high-voltage power transmissionline.