The invention discloses a knee-joint prosthesis which comprises a thighbone part and a tibia part. The thighbone part comprises a condyle groove. A cam is arranged at the rear portion of the condyle groove. The tibia part comprises an internal condyle support surface and an external condyle support surface, wherein the internal condyle support surface is arranged at the left side and the external condyle support surface is arranged at the right side. An upright is arranged between the internal condyle support surface and the external condyle support surface. The upright matches with the condyle groove. The knee-joint prosthesis is characterized in that the outer side of the surface of the rear portion of the upright is provided with a first cambered surface, and the inner side of the first cambered surface of the surface of the rear portion of the upright further is provided with a second cambered surface. A third cambered surface and a fourth cambered surface are arranged at the corresponding positions of the cam, wherein the third cambered surface and the fourth cambered surface match with the first cambered surface and the second cambered surface. The first cambered surface is capable of matching with the third cambered surface to guide a thighbone to conduct extorsion relative to a tibia. The second cambered surface is capable of matching with the fourth cambered surface to limit the thighbone to conduct extorsion relative to the tibia. The knee-joint prosthesis has the advantages of being capable of achieving accurate simulation of knee-joint flexion and extension motions by adopting actual means, safe and reliable, and capable of meeting higher requirements of a patient and simultaneously enabling products to have market value.