Abstract: To reveal the mechanical mechanism of invert arch uplift in red-bed soft rock tunnels in northwestern China, this study systematically analyzed the physical and mechanical properties of red-bed soft rock formations through laboratory experiments. Numerical simulations were conducted to investigate the effects of four key factors:swelling force, creep behavior, invert arch stiffness, and in-situ stress. The results show that:(1) The mineral composition and fracture distribution of red-bed soft rock lead to low strength, water-induced softening, swelling, and disintegration characteristics; (2) Increased water content significantly reduces the shear strength and residual shear strength of the rock mass;(3) Under high confining pressure, it is difficult for the rock to enter a creep state. Therefore, during tunnel excavation, it is essential to understand groundwater variation law and promptly implement effective support to mitigate rock creep.Sensitivity analysis of influencing factors reveals that the uplift of the invert arch is most sensitive to swelling force, followed by creep duration, in-situ stress, and invert arch stiffness. Accordingly,the control of swelling force should be a key focus during the design and construction of invert arch in red-bed soft rock tunnels.