Abstract: A three-degree-of-freedom water hydraulic artificial muscle mechanical joint with a serial-parallel hybrid model was designed based on the motion mechanism of human shoulder joint. According to the output torque range of the human shoulder joint, the mechanical joint output torque range were designed, and the parameters of water hydraulic artificial muscle were calculated to match the joint. According to the force displacement characteristics of water hydraulic artificial muscle under different working pressures, the relationship between rotation angle and torque was analyzed. A three-degree-of-freedom joint test system was designed and set up. This joint test system can achieve three-degree-of-freedom turning motion under a certain torque, which provides the conditions for further research on the motion control and maneuverability of the underwater manipulator.