Unified modeling for the kinematics analysis of a parallel hip joint manipulator (PHJM) is proposed, and structural parameters of the PHJM are optimized based on the unified model for obtaining low-velocity driving performance. Based on the finite element theory, a unified model for kinematics analysis is established, and the Monte Carlo method is subsequently proposed to solve the workspace for the PHJM. To optimize the workspace, a 6 surface-14 point (6 S-14 P) method is proposed to judge whether the workspace includes the task space. The structural parameters are further optimized to obtain low-velocity driving performance, and the motion performances of the PHJM with the optimal parameter are numerically simulated. The velocity simulation results demonstrate that the maximum relative velocity of the PHJM with the optimal parameter decreases by 23.2%. The unified kinematics analysis and low-velocity driving optimization effectively improve the performance for the PHJM and enrich the optimization theory for parallel manipulators with high velocities and given tasks.