The invention discloses an adjustable passive hydraulic oil cylinder which comprises a main body, a
piston, a side pressing cavity, a buffer cavity, a side pressing oil path, a buffer oil path, a control oil path and an overflow adjusting device; and the overflow adjusting device comprises a valve core, a spring and a double-screw bolt which lean against one another successively, and the amount ofcompression of the spring can be adjusted by rotating the double-screw bolt. By implementing a side pressing process, the
piston driven by a side pressing counteraction force moves upward, so that the
oil pressure in the side pressing cavity is increased; when the elastic force of the spring is overcome by the
oil pressure and the valve core moves, and the side pressing oil path is conducted, sothat oil in the side pressing cavity flows into the buffer cavity; and after side pressing, the
piston moves downward to compress the buffer cavity, so that oil in the buffer cavity returns to the side pressing cavity through a buffer oil path. The
oil pressure in the side pressing cavity conducts the side pressing oil path by overcoming the elastic
potential energy of the spring, and the amount of compression of the spring is adjusted by rotating the double-screw bolt, so that the side pressing vigor can be controlled, and therefore, the service life of the device is prolonged.