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The parallel mechanisms have both 2T1R and 2R1T motion mode were synthesized by using the theory of displacement manifold. The characteristic of a typical variable freedom kinematic chain was analyzed. The structure of the mechanism was constituted with three legs. Two of them were kinematic chain with four and six degrees freedom, respectively. And the other one leg was a variable freedom kinematic chain. A mechanism had both 2T1R and 2R1T motion mode was given for an example. The freedom of the mechanism in different motion mode was verified. The transform configuration of the mechanism between different motion modes was verified feasible by using screw theory. The results showed that the new parallel mechanism had two modes: 2T1R and 2R1T. At the general configuration of the two motion modes of the mechanism, the new type of mechanism can be controlled by using three active joints. At the transformation configuration of two modes of motion of the mechanism, two revolute joints of leg 2 that were connected with moving platform and fix ground respectively were collinear, the degree of freedom of the mechanism was 4 at that configuration. The auxiliary active joint was added in the branch 1, which was only applied when the mechanism motion mode was transformed, and then the motion mode of the parallel mechanism can be transformed between 2T1R and 2R1T.