Abstract: For the water-rich soft rock engineering, the damaged and saturated state of rock significantly influence its mechanical properties, affecting the stability and safety of the project. The damaged state of phyllite was assessed and classified through uniaxial compression and permeability tests conducted under various stress levels. As the applied stress level increased, the development of microcracks within the samples intensified, leading to greater damage and an increase in the permeability. After saturation, continuous water immersion caused a reduction in mechanical properties, including peak strain, compressive strength, and elastic modulus. This reduction gradually diminished over saturation time and eventually stabilized at a lower level. In the permeability tests conducted on phyllite considering different damage states, the corresponding permeability coefficients under long-term water-rich condition were lower than that in the natural state, with a maximum decrease of 3.988×10⁻⁸ m/s. Long-term water-rich conditions increased internal argillization, which blocked seepage channels and reduced the permeability coefficient. However, as the damage state intensified, the difference in permeability coefficient between long-term water-rich conditions and the natural state gradually diminished. As the damage degree increased (i.e., higher stress level), fracture development intensified, leading to the migration of previously blocked clastic particles and the formation of new microscopic seepage channels. The mechanical properties of phyllite under long-term water-rich conditions were always lower than those in the natural state. Compared to the natural state, the peak strain and compressive strength of the damaged phyllite under long-term water-saturated conditions decreased by up to 9.5% and 43.4%, respectively. The gap in mechanical properties of phyllite between long-term water-rich and natural conditions gradually diminished with increase in the damage degree.