Based on the structural characteristics and motion characteristics of the upper limbs of human body, a lightweight humanoid rope-driven collaborative robotic arm structure was proposed and the 3-RRRR-(UPU)wrist parallel mechanism was designed. The center lines of the arcuate link hinge intersected on diagonals, and the intersection performed spherical pure rolling with the dynamic platform relative to the static platform, and an elliptical motion trajectory was formed. A virtual circle approximating ellipse error model was constructed, then the motion error data of the parallel mechanism under different sizes was processed with interpolation optimization treatment, finally the optimization model was obtained. The dynamic and static coordinate systems on the dynamic and static platforms were established respectively, a kinematics diagram of the parallel mechanism was constructed and the forward kinematics analysis was completed. Through the analysis of the forward kinematics, the relationship between the length of the rope and the position of the dynamic platform at the parallel mechanism end was deduced. Finally the correctness of the analysis result was verified by the verse kinematics.