A
harmonic reducer, a mechanical arm and a
robot, the
harmonic reducer comprising a circular spline, a flexspline and a wave generator, wherein the wave generator comprises a
cam and a flexible bearing; a bearing outer ring is provided on an outer
peripheral wall of at least one side of the
cam, and the
cam is rotationally connected to the bearing outer ring; and an outer
peripheral wall of the bearing outer ring is connected to an inner
peripheral wall of the circular spline. In the present invention, the bearing outer ring is arranged on an outer peripheral wall of at least one end of the cam, and the cam serves as a bearing inner ring, such that parts and components are reduced; and under the same
bearing capacity, the bearing outer ring limits the flexspline and the flexible bearing, a sealing ring is omitted, and no additional connecting component or fixing component needs to be used for fixing the flexspline, thereby simplifying the process and reducing the volume and the weight of the
harmonic reducer. The harmonic reducer in the present invention can be directly connected to an
electric motor, and no additional bearing is needed, which reduces the
axial length when the harmonic reducer is connected to the
electric motor, and does not reduce the power of the
electric motor, thereby further achieving the aim of
miniaturization, and thus the cost is reduced and promotion is facilitated.