The paper aims to research motion performance and workspace of a six DOF 3-PUPU parallel mechanism. The freedom degree of the moving platform of the parallel mechanism was calculated by using the modified (G-K) formula. And the kinematics and inverse kinematics equation of mechanism was established. Then the 3-PUPU parallel mechanism and structure block diagram were established by using the SimMechanics function module of Matlab/Simu- link; and the workspace of the 3-PUPU parallel mechanism was obtained by programming according to restriction condition of rod length. The workspace of the parallel mechanism had large range, regular shape, compact structure and is free from holes. 3-PUPU parallel mechanism has good performance of workspace.