Abstract: The substructure online hybrid test is one of the most effective methods to reproduce the complex seismic behavior of large scale structures. This paper summarizes the major challenges that have been solved in the past thirty years. The dynamics of a target structure can be solved by a stable and accurate time integration algorithm which shall provide an explicit displacement command for the tested substructure and be better have the capability to mitigate the error introduced by the experimental domain. The second challenge is to coordinate the implicit numerical substructure with the explicit tested substructure, for which either a stiffness predicting scheme or a predicting and correcting scheme shall be employed. Finally, the boundary conditions between substructures shall be precisely exerted on each substructure, which might be difficult for tested substructures because of the limited resolution and number of loading devices. To this end, the flexible loading scheme based on overlapping domains and the force-displacement mixed control are developed. To maximize the capacity and to improve the accuracy of the online hybrid test, the resources of different labs and finite element software are expected to be incorporated into the system, which initiate three generations of scalable frameworks for hybrid tests. The flexibility, extensibility and accuracy of the proposed three frameworks have been demonstrated by a series of real applications to reproduce the seismic responses of complex structures to collapse.