A knee joint prosthesis is adapted for interconnecting a prosthetic lower leg and a prosthetic thigh. The knee joint prosthesis includes a knee seat disposed under and connected to the prosthetic thigh, a connecting seat disposed above and connected to the prosthetic lower leg, a link assembly, and an adjusting unit. The link assembly includes a plurality of links each connected pivotally to the knee seat and the connecting seat in such a manner to allow the knee joint prosthesis to change between an elevated position and a flexed position. The adjusting unit is disposed in the knee seat, and is operable to cooperate with the link assembly to adjust difficulty level of changing the knee joint prosthesis between the elevated and flexed positions.
