The utility model discloses a transformer theftproof whelk cap and special spanner thereof relates to transformer technical field. The utility model discloses a nut body, nut body are equipped with the screw thread blind hole, and the outer wall of nut body has a tapering, the outer wall of nut body is the glossy conical surface. The utility model discloses can reduce the emergence of stealing oily phenomenon, avoid unusual reduction of oil in the transformer and cause great electric power accident.