Based on Screw Theory and KutzbachGrübler Formula, the movement character was analyzed and DOF was caculated about parallel mechanism of 4UPU. Kinematic joints being arranged, four prismatic joints were chosen as the inputs. The equations of position were built in order to judge sigularity by Jacobian algebraic method, thereby the sigular positions were obtained. By the equations of position and constraint conditions, the workspace of this mechanism was calculated on condition that the posture is certain and singularity is inexistent. The results show that singularity configuration is related with attitude angle and platform of structural parameter and workspace of this mechanism is uncontinuous and related with attitude angle.