Abstract: The sampling robotic arm is one of the important tools to realize the lunar surface sampling, and the joints are the basis of the flexible movement and the precise positioning of the arm. In order to meet the special requirements of the lunar surface sampling task for the dustproof, the high temperature resistance and the light weight of the joint, a joint design scheme of the 2K-H planetary reducer plus the harmonic reducer driven by the permanent magnet synchronous motor is proposed. In the scheme, the magnetostatic torque of the motor provides the joint braking torque, and the feedforward torque compensation control method is used to eliminate the speed fluctuation caused by the magnetostatic torque and save the brake configuration. By controlling the gearbox transmission backlash, the motor stator shell interference and the gasket thickness, the thermal matching of the joint in the temperature range of -100~160℃ and the dustproof goal are achieved. The simulation analysis and the prototype test verify that the joint design can meet the task requirements for the lunar sampling.