Due to a large number of electrical cables in the joints of traditional space manipulator, the assembly, testing and maintenance are very inconvenient. In this paper, a modular joint with light weight and wireless communication link is developed to solve the above problem. The performance of the joint is firstly determined according to task requirement. Then, the mechanical structure is designed to meet the performance requirement. It is mainly constructed by a brushless DC motor, harmonic reducer, bearing, and supporting structure. The electrical sub-system includes sensors, servo controller and WIFI communication link. Multiple sensors, including three hall sensors, an incremental magnetic encoder, an absolute magnetic encoder, and a torque sensor are installed in the joint. The vector control is used for motor. The WIFI communication link is designed for the communication between the central controller and the servo controller. Therefore, the task command can be sent through the WIFI link. Electrical cables between the central controller and joint servo controller are not required. Finally, the developed joint is tested on a test platform. The experimental results verify the performance of the joint.