Abstract: The control methods are mostly used for the fault tolerance of parallel mechanism at present. However, there are few studies on structure design of parallel mechanism with actuation fault tolerance. To quantitatively analyze the influence of driving force invalidity on the operability performance of mechanism, an operability invalidity index was proposed for evaluating the driving force invalidity of the branches of the parallel mechanism based on the Jacobian matrix. The driving identity condition of the redundant parallel mechanism stated as “the driving force screw of the redundant parallel mechanism was expressed in the same form in a fixed coordinate system, and the linear independent number of the driving space was equal to the degree of freedom. If any driving force screw（driving force invalidity fault） was removed, the driving space would not degrade”, that satisfied the driving force invalidity tolerance was given. Based on the screw theory and guided by the driving identity condition, which promised that the driving force screws can be mutually substituted, a type synthesis method of redundant parallel mechanism was proposed, and a 3 R DOF type of redundant parallel mechanisms with actuation fault tolerance was synthesized. The actuation fault tolerance of the（4-RRR）_Ⅰ redundant parallel mechanism synthesized was evaluated by using the proposed operability invalidity index, which verified that the synthesized mechanism had the drive force invalidity tolerance. The research result can provide a way to solve the driving force invalidity of parallel mechanism, and can enrich the types of parallel mechanism, which provided a theoretical basis for the application and development of redundant parallel mechanism with actuation fault tolerance.