The workspace and the kinematic transmission play important role on the design and optimation of the eblow joint. In this paper, a novel humanoid robot elbow joint based on 2-DOF orthogonal spherical parallel mechanism is proposed. Position of elbow joint is analyzed using the vector method and projection theory. The kinematic balance equation of the eblow joint is established by analyzing the relationship of its input and output velocity. The kinematics transmission evaluation index and the global kinematic transmission evaluation index of the elbow are defined, and the distribution of the global kinematics transmission evaluation index in the workspace is drawn. And rotation ability of the elbow joint is analyzed. The analytical results indicate the elbow has advantages of big volume, smooth boundary, good kinematic transmission, strong rotation ability, which can provide theoretical base for the applications of the elbow.