The invention relates to the technical field of robots, and provides a high-bearing universal joint, a mechanical arm joint and a flexible mechanical arm. A second slide ball comprises a first cavitywith the inner surface as a spherical surface; a first slide ball is rotationally arranged in the first cavity, and can slide along the inner surface of the first cavity; a ball base comprises a second cavity with the inner surface as a spherical surface; and a second slide ball is rotationally arranged in the second cavity, and can slide along the inner surface of the second cavity, so that the contact area between the first slide ball and the second slide ball and the contact area between the second slide ball and the ball base are guaranteed, and the load capacity is improved. A first limiting structure and a second limiting structure are provided for limiting rotation of the first slide ball along the latitude line and rotation of the second slide ball along the latitude line, so thatthe problem of underactuation of a general ball hinge structure is solved under the precondition of realizing universal rotation through combination of a motion between the first slide ball and the second slide ball and a motion between the second slide ball and the ball base.