Coupling is the significant characteristic of parallel mechanism,while it is just the coupling that brings about much difficulty for the configuration design,theoretical analysis and the development of the control system of the parallel mechanism. And recently,the research on the decoupled parallel mechanism becomes one of the research hot points in the mechanism fields. In this paper,a type synthesis method for the translational decoupled parallel mechanism( TDPM) is proposed based on the screw theory. To achieve the decoupling characteristics of the translational parallel mechanism,the translational decoupled criterion for type synthesis of the branches are presented in this paper. According to this criterion and the realization conditions of rotational degree of freedom of the mechanism proposed former,a large number of branches for the TDPM are obtained. Taking the three degrees of freedom( DOFs) TDPM as an example,the process of type synthesis is discussed in detail. Using this proposed type synthesis method,a serial of translational decoupled parallel mechanisms, including but not limited to all the existing typical 3-DOF TDPMs, are obtained, which identifies the correctness and effective of the method. The contents of this paper provide a reference and possess significant theoretical meanings for the synthesis and development of the novel decoupled parallel mechanisms. Coupling is the significant characteristic of parallel mechanism, while it is just the coupling that brings about much difficulty for the configuration design, theoretical analysis and the development of the control system of the parallel mechanism. And recently, the research on the decoupled parallel mechanism becomes one of the research hot points in the mechanism fields. In this paper, a type synthesis method for the translational decoupled parallel mechanism (TDPM) is proposed based on the screw theory. To achieve the decoupling characteristics of the translational parallel mechanism, the translational decoupled criterion for type synthesis of the branches are presented in this paper. According to this criterion and the realization conditions of rotational degree of freedom of the mechanism proposed former, a large number of branches for the TDPM are obtained. Taking the three degrees of freedom ( DOFs) TDPM as an example, the process of type synthesis is discussed in detail. Using this pr oposed type synthesis method, a serial of translational decoupled parallel mechanisms, including but not limited to all the existing typical 3-DOF TDPMs, are obtained, which identifies the correctness and effective of the method. The contents of this paper provide a reference and possess significant theoretical meanings for the synthesis and development of the novel decoupled parallel mechanisms.