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The safe disposal of high-level radioactive waste (HLW) is a major issue to ensure environmental protection and the sustainable development of the nuclear energy industry; it is also an equally important issue regarding nuclear safety. Deep-buried geological disposal is recognized worldwide as the safest and most feasible way to protect human beings and the environment. To satisfy the research functions, most underground research laboratories (URLs) for geological repositories are buried deeply, and their layout is quite complex. To research nonlinear deformation characteristics and failure mechanism of deep underground caverns in the process of construction, we developed an intelligent true triaxial non-uniform loading/unloading model test system. The system has the advantages of a large rated output, starting from zero pressure, cyclic loading and unloading, high loading accuracy and displacement test accuracy, and arbitrary adjustment of device size. We carried out a true three-dimensional physical model test, taking the URL for the deep-buried geological disposal of HLW in Beishan area, Gansu Province as the prototype. The nonlinear deformation characteristics and the law of displacement change of the underground laboratory caverns are reproduced. We observed the whole process, from the appearance of micro cracks to the expansion of the cracks and the collapse of the cavern group. This provides an important experimental basis for optimizing the design and construction of URL for the deep-buried geological disposal of HLW. The value and slope of displacement calculated by the numerical simulation are mainly the same as the experimental results of the geological model test, which validates the accuracy and reliability of the model test system in this study.