In order to realize the aim of structure and function bionics of the shoulder joint, 3-PCSS/S (PC stands for the prismatic pair with the circular guide, S stands for the spherical pair) spherical parallel mechanism is proposed as the prototype for the shoulder joint, and the mechanism optimization and bionic design are performed. The PC prismatic pair with the circular guide is equivalent to the revolute pair, the inverse kinematics of the mechanism is solved and the Jacobian matrix is obtained. According to the determined constraint condition of the orientation workspace, choosing the number of the points in the orientation workspace as the optimization object, the global optimization on the parametric variables of the mechanism is carried out using genetic algorithm. The bias design idea is proposed which expands the range of the output angle of the mechanism, and the flexibility of the shoulder joint is improved. The research possess theoretical guidance significance and practical application value on the bionic design and the entity development of the shoulder joint of the humanoid robot.