A knee joint orthosis, comprising a thigh frame (20) to be worn on the thigh of a lower limb and a calf frame (10) to be worn on a calf; the thigh frame (20) is connected to the calf frame (10), and can rotate between a first position and a second position relative to the calf frame (10) around a first axis at a connection position of the thigh frame (20) and the calf frame (10); when the thigh frame (20) is at a first position, the knee joint orthosis is suitable for the lower limb at a normal standing position; the thigh frame (20) can also conduct a second relative rotation relative to the calf frame (10), and an included angle between the first axis and the rotation plane of the second relative rotation is in the range of 0 degree to 15 degrees; a connection structure between the thigh frame (20) and the calf frame (10) comprises an adjustment mechanism (31) and a connection hinge (41); and the thigh frame (20) rotates relative to the adjustment mechanism (31), and conducts the second relative rotation via the connection hinge (41). Owing to the connection hinge (41) and the adjustment mechanism (31), the knee joint orthosis is suited to the relative internal rotation and external rotation between the thigh and the calf in the movement of a human lower limb, and is thus more suitable for human engineering and kinesiology.