The invention relates to a method for vertically entering a strong electric field along an insulator string and a tool used by method. An equal potential operator vertically stands on an anti-tension insulator string, carries a walking stick type insulator steel cap fixing clamp with each of two hands to clamp a steel cap of another anti-tension insulator string and vertically enters the strong electric field along the anti-tension insulator string; when moving along the anti-tension insulator string, the equal potential operator releases the clamp farther away from a live lead wire and slowly puts the clamp close to another clamp; after the two clamps clamp the steel cap of an insulator simultaneously, the equal potential operator moves along the anti-tension insulator string in a two-crossing and three-short-circuit manner to arrive at the working position; each walking stick type insulator steel cap fixing clamp comprises a rod body and a clamping mechanism arranged at the lower end of the rod body; the steel cap of the insulator is clamped or released by the clamping mechanisms. According to the method disclosed by the invention, the physical exhaustion is greatly reduced; furthermore, the operator feels more comfortable in an operating process; the method is particularly suitable for a +/-800kv direct-current ultrahigh-voltage power transmission line.