In this technical brief, the resonance problem of a robot joint is analyzed. By establishing the electromechanical coupling dynamic equation of the robot joint, the natural vibration characteristics of the electromechanical coupling system are calculated, and the resonance is analyzed by combining the modal energy and Campbell diagram. It is found that when the meshing frequency coincides with the seventh- and eighth-order natural frequencies, resonance is easy to occur. The influence of different parameters on natural characteristics is analyzed. The increase of torsional stiffness and meshing stiffness will increase the natural frequency. Different control algorithms will have different impacts on the transmission system, and fuzzy control is better than double closed-loop control.