A tumble-resistant knee joint includes a knee carrier, a main base, and a coupler connected to each other. The knee carrier includes a connection piece and two connection bars to couple to an upper portion of the main base. The coupler includes coupler recesses formed in one side thereof corresponding to extensions of grips to receive push blocks therein and has two coupling bolts extending through a lower portion of the main base to allow the coupler connected to the lower portion of the main base. The main base receives therein an axle, which is provided, respectively and in sequence from a center thereof toward two opposite ends, with two bearings, two one-way bearings, two bushings, and two grips. The grips include extensions that cooperate with the push blocks to selectively grip or release the axle. The one-way bearings constrain the rotation of the axle to be in one direction.
