Abstract: This article presents the singularity analysis and synthesis of a 3-DOF(degree of freedom) mobile parallel manipulator with 3 limbs and 5 joints via screw theory and linear geometrical method.We studies the singularity of structure and the singularity of configuration of active(actuating) joints.Linear geometrical schemes are given to illustrate the displacement of singularity.This analysis lays a foundation for further research on kinematics and dynamics of this kind of parallel manipulators.