Abstract: This study aims to address the large deformation in carbonaceous phyllite tunnels under high in-situ stress. Taking the carbonaceous phyllite from a large-deformation section of a plateau railway tunnel in southwestern China as the research object, laboratory triaxial compression and creep tests were conducted. Based on the test results, a constitutive model accurately describing the creep behavior of carbonaceous phyllite was established. This creep model was applied in numerical simulations to optimize the support structure, thereby developing a comprehensive technology for large deformation control, which was subsequently validated through field tests. The results indicate that: (1) The average maximum horizontal stress in the large-deformation section is 13.05 MPa. With low strength and high susceptibility to softening, carbonaceous phyllite may undergo large deformation at a depth of approximately 400 m under high tectonic stress. (2) Compared with the classical Burgers model, the non-stationary Burgers model developed based on experimental data demonstrate shigher fitting accuracy and more accurately characterizes the creep properties of carbonaceous phyllite. (3) Numerical simulations show that employing HW175 steel arches or double-layer I20a steel arches (spaced at 0.6 m per frame) can effectively control deformation. Field monitoring data from the test section further reveal that, compared with HW175 steel arches, the double-layer steel arch offers limited improvement in controlling sidewall and vault deformation.