For a gas-solid insulation system with direct current (DC) voltage, the surface charge accumulation and decay phenomenon are directly related to the capacitive-resistive electric field transition process. The accumulated charges will affect the electrical insulation performance of a gas-solid insulation system, which is a challenge for the development of DC gas-insulated metalenclosed transmission line (GIL) equipment. In this paper, a study of the surface charge accumulation characteristics for a DC GIL insulator in the electric field transition process is presented. The charge accumulation model for the gas-solid insulation system was established with consideration of the bulk charge conductivity in the solid dielectrics, the ion conductivity in the weakly ionized gas, and the charge conductivity at the interface. A surface potential measurement system was then built. The charge accumulation model was verified by measurements of the surface potential on a cylindrical insulator sample, and the charge accumulation characteristics on the surface of the GIL insulator were investigated. The simulation results indicate that the accumulated homopolar charges led to the decrease of the electric field strength near the conductor by 9.4% and the increase of the electric field strength near the GIL shell by 23.5%. The concave surface of the insulator mostly accumulated heteropolar charges, which led to an increase in the electric field intensity by 5.5%. The transition of the charge accumulation mechanism with the variation of the bulk conductivity was also analyzed. The convex surface of the insulator accumulated homopolar charges, and the concave surface mostly accumulated heteropolar charges when the bulk conductivity was between 10 −14 and 10 −17 S/m. However, with the further reduction of the bulk conductivity, the mechanism of the charge accumulation gradually became dominated by ion conductivity in the SF 6 gas.