Abstract: During the construction of high-level radioactive waste (HLRW) repositories, stress disturbance is prone to induce plastic responses and strain localization in the excavation areas, generating preferential flow paths for radionuclide migration and threatening the safety of repositories. This study drew on a field case of an underground laboratory for HLRW repositories in argillaceous rock and established a finite element numerical model using an advanced elasto-viscoplastic constitutive model with reference to the interaction between surrounding rocks and the support system. Orthogonal experimental design was then employed to investigate the effect of support stiffness modulus, support installation times, and excavation rates on strain localization. Results reveal that: ① Both sides of the tunnel opening are high-risk zones for excavation damage and strain localization, where preferential flow paths are likely to develop and threatens the long-term stability of the disposal repository; ② Installation time of supports and excavation rates significantly affect the development of excavation damage zones. Delayed installation would significantly enlarge plastic zones. This study could offer references for stability analysis of HLRW repositories in argillaceous rocks in China.