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The purpose of this article is to investigate the rheological deformation behavior of soft rocks subject to the combination of externally applied compressive pressure and water-softening effects. To achieve this goal, a series of mechanical tests on soft rocks were performed by using a customized meso-mechanical triaxial test system consisting of a bidirectional servo confining pressure loading subsystem and a water pressure chamber. The system has the capability of simulating the actual compressive stress and water environment of soft rocks in engineering practice. The experimental results show that, under compressive stresses, water-softening effects could significantly increase the deformation rate of the soft rocks, ultimately lead to a larger deformation of the rocks. To further understand the combination of compressive pressure and water-softening effects on the deformation behavior of the soft rocks, an elastoplastic damage model was developed. It shows that the model can reproduce the experimentally observed deformation behavior of soft rocks. In addition, it reveals that, with the rock-water interaction, the deformation process of the compressed soft rocks can be described as the change from the attenuation state to the steady state of rheological deformation.