By taking the 3-SPT-S Parallel manipulator as the research objective, conducted position analysis of the mechanism, the kinematical model and mathematical model were developed. The Jacobian matrix and Hessian matrix of the manipulator were derived, and the performance index of dexterity about the local velocity and acceleration was solved. The local performance indices atlas was drawn by using the mathematical software MATLAB. The change regulation of the performance indices is analyzed in different position of the parallel manipulator.