Antitheft well head cap and its special spanner

The utility model discloses a theft-proof wellhead cap equipped at a well not equipped with any equipment in an oil field and a dedicated spanner fitting the theft-proof wellhead cap. The theft-proof wellhead cap comprises a body (5) which is a screw plug one end of which is sealed and a detachable nut (2) which is fixedly connected with the outboard of the sealed end at the body (5). The theft-proof wellhead cap also comprises a protective cover (1) at the lateral plane of which is equipped a tool window (4) and which is fixedly connected with the body (5) and is located above the detachable nut (2). The dedicated spanner consists of a handle (3) and an operating part (7) consisting of a raised section (10) which corresponds to a mouth part (8) at the detachable nut (2) and a sunk section (11) which corresponds to a tongue part (9) at the detachable nut (2). Because of the protective cover (1), the detachable nut (2) can not be watched clearly and mapped. At the same time, a disassembly tool can not be mapped for an imitation manufacture. The utility model can effectively protect the well.