A novel 3-CRS parallel mechanism with six degrees of freedom is proposed and the metamorphic characteristics of 3-CRS parallel mechanism are studied based on cylindrical motion variable locked in the sub-chain. Firstly, the kinematic parameters of 3-CRS parallel mechanism are analyzed, and the closed equations of the kinematic variable are obtained. Secondly, the screw system of the sub-chain of 3-CRS parallel mechanism is analyzed, and the motion characteristics of 3-CRS parallel mechanism are mastered. Thirdly, the sub-chain constraint-screw system of 3-CRS parallel mechanism is studied in detail when the moving or rotating variables of cylindrical pair are locked. Finally, the metamorphic characteristics of 3-CRS parallel mechanism are discussed when the moving or rotating variables of cylindrical pair are locked. The results show that the metamorphic characteristics of 3-CRS parallel mechanism can be obtained by locking the cylindrical pair parameters.