[Purposes] The study aims to investigate the structural degradation factors and influencing mechanism of gently inclined soft rock tunnel bottom and explore the deformation and plastic zone development trends of gently inclined soft rock tunnel bottom under varying surrounding rock strength, attitude of rock formation, and ground stress conditions. [Methods] The mechanical parameters for numerical simulation were determined using the Hoek-Brown strength criterion and pervasive joint constitutive model. An excavation model was created. The deformation law of the tunnel was analyzed by changing the Hoek-Brown parameter, attitude of rock formation, and ground stress state. [Findings] The deep-buried gently inclined soft rock tunnel exhibits noticeable asymmetric deformation on both sides of the arch bottom. As the Hoek-Brown parameter and surrounding rock strength increase, the uplift of the arch bottom reduces, and the asymmetric deformation on both sides of the arch bottom is weakened and tends to be symmetrical. When surrounding rock strength is low, the mixed shear plastic zone mainly concentrates at the arch bottom, while matrix shear failure primarily occurs at the side walls. This shear failure range decreases as surrounding rock strength increases. For dip angles of 0°~30°, the uplift at the tunnel bottom decreases as the rock dip angle increases. Additionally, the depth of the plastic zone at the arch bottom progressively decreases. As the rock inclination angle increases, both the asymmetric deformation and deformation magnitude at the tunnel bottom increase. The mixed shear plastic failure zone at the arch bottom extends to greater depths. Increasing lateral pressure coefficient and burial depth results in larger deformation magnitudes and rates at the tunnel invert compared to other locations. Changes in burial depth primarily affect the volume and depth distribution of the surrounding rock’s plastic zone, whereas changes in the lateral pressure coefficient mainly impact the form of plastic zone distribution. [Conclusions] The deformation and failure mode of the plastic zone in a gently inclined surrounding rock tunnel are influenced by the attitude of rock formation. At low gently inclined angles, the arch bottom experiences significant deformation, while the shear failure of the surrounding rock joint occurs mainly in the direction of rock formation inclination. The research results can provide a reference for determining the unfavorable deformation position and optimizing support schemes in the construction process of similar projects.