The construction of a new type of power system with new energy as the main body has become an inevitable choice to realize the national “double carbon” strategic goal, and HVDC transmission technology is an important physical support for the realization of new energy grid connection and the safe and stable operation of large power grids. The gas insulated transmission line (GIL) can meet the special transmission needs of offshore wind power transmission and offshore island power supply, crossing rivers and lakes and urban power corridors, and is the key equipment for the future DC power grid. Compared with AC pipeline equipment, the surface charge accumulation problem of basin insulator under DC stress is more serious.This research investigates the impact of SiC coatings with varying thickness and composition on the prevention of surface charge buildup and enhancement of DC flashover voltage. The nano-silicon carbide (SiC) and epoxy resin (EP) were uniformly mixed to obtain a coating, which was uniformly coated on the insulator sample to obtain a coated insulator sample. The potential values of each point on the surface were measured, and the surface charge distribution was obtained by inversion algorithm. The experiments conducted demonstrate that the coating effectively optimize the surface charge situation and electric field distribution, while simultaneously increasing the breakdown voltage. Increased mass fraction of doped filler particles, the surface charge density achieves its minimum value when the SiC concentration is 20wt %. As the coating increases from 100 um to 300 um and then to 500 um, the charge does not decrease monotonically, but a minimum value appears in the 300 um sample test. And the experimental results show that any coating with any parameter can improve the DC flashover voltage of insulator samples to varying degrees. The research in this paper can provide theoretical basis and technical support for the optimal design of surface insulation of DC GIL basin insulator.