Kinematically indeterminate structure is a type of special structure that consists of internal mechanism. This paper mainly proposes a unified approach for the motion analysis of kinematically indeterminate structure based on inextensional mechanism, which is achieved by the equilibrium matrix SVD. The physical meaning of inextensional mechanism is studied and the detail procedure for the simulation algorithm is presented. Further more, it is applied to trace the motion paths of unfolding process of an expanded octahedron tensegrity unit and the deployment of radial retractable structure. Simulation results show the validation and efficiency of the presented method.