Humanoid robots are a hot research topic in robotics nowadays and show broad application prospects. Among the various components of humanoid robots, the wrist is essential as it enables the completion of complex motions. Compared to the serial configuration, the wrists with parallel configurations show the advantage of compactness and high stiffness. In this paper, the kinematic and optimal design of a robotic wrist with a 2SPS-RR parallel mechanism are performed. Firstly, the position, velocity, and singularity are analyzed and the workspace is presented. Secondly, an optimization model that considers multiple performance indexes is proposed. The function is simple to calculate, which takes into account the effects of the area of the workspace, the expected boundary and the singular trajectory. Then, a global optimization of the mechanism is conducted based on the design parameters, and a set of optimal parameter values is obtained. The results indicate that the desired workspace of the mechanism is distant from the singular trajectory with the optimized parameters, and the coverage of the workspace relative to the desired workspace is considerable. Furthermore, the sensitivity and condition number of the design parameters are analyzed. Finally, the driving force and driving speed of the mechanism are analyzed in conjunction with the optimal parameters, which provides a theoretical reference for the design of the humanoid robot wrist.