Hydraulic oil cylinder with self-locking protection device

Provided is a hydraulic oil cylinder with a self-locking protection device. Relates to the technical field of hydraulic cylinders. The structure is reasonable, and the locking effect is reliable. Comprising a cylinder body and a piston rod, one end of the piston rod is arranged in the cylinder body in a penetrating mode, a connecting base is arranged at the other end of the piston rod, the self-locking protection device comprises a shell and a locking rod, one end of the locking rod penetrates through the shell, and the other end of the locking rod is fixedly connected with the connecting base. A casing pipe is arranged in the shell and located outside the locking rod, a first gap exists between the inner wall of the casing pipe and the outer wall of the locking rod, a second gap exists between the outer wall of the casing pipe and the inner wall of the shell, a plurality of penetrating holes facing the axis of the casing pipe are formed in the casing pipe, locking blocks are arranged in the penetrating holes