The inverse position equations are formed

and the velocity equation containing the actuator and the end effector velocities

and the analytical express of Jacobin matrices are derived for the 3PSS-S spherical parallel manipulators.Based on those Jacobin matrices

the contours method was adopted for analyzing the singularity loci of 3PSS-S spherical parallel manipulators.The influence of structure parameters of static platform on singularity loci of parallel manipulator is studied.