The invention discloses an oil well mouth protecting device which comprises an anti-theft cover with an opening, a connecting piece, a connecting rod, an operation piece and a limiting piece. The opening is used for corresponding to a flange of an oil well mouth. A hole is formed in the anti-theft cover. A protruding part which is used for abutting against the flange is arranged on the inner side wall of the anti-theft cover. A limiting part placed below the protruding part is arranged on the inner side wall of the anti-theft cover. The connecting piece is fixedly connected to the side wall of an oil well mouth pipeline. The connecting rod is provided with an upper end and a lower end. The position between the upper end and the lower end of the connecting rod is hinged to the connecting piece. The operation piece is connected to the upper end of the connecting rod. The operation piece can drive the connecting rod, so that the connecting rod rotates around the connecting piece. The operation piece and the oil well mouth pipeline can be fixed, and the operation piece corresponds to the position of the hole. The limiting piece is connected to the lower end of the connecting rod. The oil well mouth can have anti-theft and anti-damage functions.