Dismounting or fastening device

The utility model discloses a dismounting or fastening device which is used for demounting or fastening a screw and a nut which are screwed relatively, and key slots are respectively formed in the screw and nut; the dismounting or fastening device comprises a first wrench, a second wrench, a jack and a spherical connecting piece, wherein the first wrench comprises a first clamping block, the second wrench comprises a second clamping block, the jack is fixed on the first wrench, the spherical connecting piece is connected to the jack and the second wrench, the first clamping block is arranged inside the key slot of the screw in a clamping manner, the second clamping block is arranged inside the key slot of the nut in a clamping manner, and when the jack acts, the second wrench is driven by the spherical connecting piece to rotate relative to the second wrench. Therefore, the nut is enabled to rotate relative to the screw, so as to dismount or fasten the screw and the nut.