An artificial knee joint includes a joint support having upper and lower ends jointed to outside links and an upper link respectively; a brake block having upper and lower jointing holes respectively jointing a lower end of the upper link and a connector, and having an upper portion forming a positioning slot; a hydraulic cylinder arranged inside the brake block and having an upper end coupled to the joint support; a connector having a lower portion connected to a shank and an upper end portion through which a positioning axle extends; and outside links having an upper end jointed to an upper jointing hole of the joint support and a lower end jointed to a jointing hole of the connector. A cylinder barrel, a piston, a resilient element, and an adjusting bolt are arranged inside the connector and the piston is set against a lower end of the brake block.