The invention discloses a hydraulic cylinder internally provided with a magnetostrictive displacement sensor, comprising a cylinder barrel, a piston, a piston rod and the displacement sensor and further comprising a cylinder body end cover and a cylinder head; the cylinder body end cover is arranged at the end of the cylinder barrel and is communicated with the cylinder barrel; oil port seats are positioned at both ends of the cylinder barrel respectively; the piston is mounted in the cylinder barrel in a sealing manner; the piston rod is connected with the piston; a magnetic ring is fixed at the place of an inner cavity of the piston rod; the displacement sensor passes through the inner cavity of the piston rod and is clamped on the cylinder body end cover in the sealing manner; the top of the cylinder head is pressed on the displacement sensor and is fixed with the cylinder body end cover. According to the cylinder disclosed by the invention, the action area of hydraulic oil to the end surface of the displacement sensor is reduced effectively, the acting force of the oil pressure is lowered, and the structure reliability is improved; moreover, the cylinder is convenient to repair, high in displacement detection accuracy and long in service life.