A hydraulic jack is provided which comprises a piston cylinder, a piston rod, an oil passage switching valve and an internal cylinder. The oil passage switching valve is provided with an oil outlet; a one-way valve assembly preventing the backflow of the oil outlet passage is disposed between the first oil inlet passage and the oil outlet passage; a return oil inlet passage is disposed at the bottom of the piston head; a return oil chamber in communication with the return oil inlet passage is disposed inside the piston head; a return oil outlet passage communicating the return oil chamber and the piston cylinder oil storage chamber is disposed on the piston head; a one-way return oil assembly is mounted in the return oil chamber, thus the hydraulic oil does not enter the hydraulic area and finally the top plate will not rise continuously along with pressing, providing overload protection.