Abstract: The safe disposal of high-level radioactive waste(HLW) is a critical challenge for the sustainable development of nuclear energy globally. Deep geological disposal, internationally recognized as a viable solution, aims to isolate HLW over long timescales(up to millions of years) through a multi-barrier system. This paper focuses on the long-term alteration of the host rock in the near-field of a deep geological repository and its prolonged impact on the geochemical environment and radionuclide migration behavior. After repository closure, the surrounding granite will undergo continuous alteration due to combined effects of decay heat, groundwater-rock interaction, ionizing radiation, and microbial activity. These alteration processes may modify the physical properties of the rock mass(e.g., pore structure, permeability, and fracture connectivity), potentially reshaping groundwater flow paths and radionuclide transport routes. Simultaneously, the dissolution of primary minerals and precipitation of secondary phases can alter the chemical conditions of the near-field groundwater. Furthermore, rock alteration may change mineral surface properties such as sorption sites, surface charge, and reactivity, and promote the generation and long-term evolution of colloids. These physicochemical changes complicate radionuclide migration, affecting diffusion and advection mechanisms within altered fracture networks and the rock matrix. From the perspective of long-term host rock alteration, this study investigates the migration, transformation, and fate of radionuclides following the closure of a deep geological repository.