<p>In this article, the multiphysics simulation model for DC-GIL (Direct-current Gas-Insulated Transmission Lines), based on the finite element method and coupling thermal, fluid, and electric fields, has been established. The electric characteristics of basin insulator in SF₆-insulated 400&#xa0;kV DC-GIL model have been simulated and analyzed. The effects of mesh sensitivity, insulating gas pressure, load current, surface conductivity and water concentration on the electric field characteristics of the basin insulators have been further investigated. The results indicate that insulating gas pressure has a relatively minor impact on the temperature and electric field strength of the insulator. The load current significantly affects the temperature and electric field strength distribution of the insulator. Simulation results show that a significant increase in electric field strength is observed at the edge of the insulator when surface conductivity is considered. Under identical conditions, the presence of 0.2% water concentration results in a maximum increase of 21.21% in the surface electric field strength of the insulator. The multiphysics coupling analysis of DC-GIL under multi-factor conditions conducted in this study provides a theoretical foundation and data support for the design and maintenance of DC-GIL systems.</p>