A prosthetic knee joint structure is provided herein. The knee join mainly contains an upper member for connecting to a prosthetic thigh, a lower member for connecting to prosthetic shin and foot, a linking device for connecting the upper and lower members, a cushion element, and a resilient device. During walking, the resilient device prevents the shin from dangling and the knee joint from sudden bending and kneeling-down. The cushion element absorbs the shock when the prosthetic leg is walking on a flat ground or slope.