The problem of gas–solid interface charge accumulation is an important reason for distorting the surface electric field and then inducing surface discharge. The temperature gradient distribution formed on the spacer during the operation of a gas-insulated transmission line (GIL) will aggravate the surface charge accumulation

further threatening the surface insulation performance of the spacer. This study proposes a thermal-dependent conductivity coating method to regulate the surface charge and electric field distribution on DC GIL spacers under an electrothermal coupling field. Under the temperature gradient

the symmetrically ring-shaped homocharges around the high-voltage electrode and the randomly cloud-shaped bipolar charges are distributed on the uncoated spacer surface. After coating TiO2/epoxy mixtures on the spacer surface

the surface charge distribution on the spacer is dramatically homogenised under the thermal gradient

no matter which content of TiO2 is used. A simulation model for the surface charge and electric field on the spacer with/without TiO2/epoxy coating under the electrothermal coupling field is established. The results are well consistent with those of the experiment. When the content of TiO2 in the coating material increases from 10 wt% to 30 wt%

the maximum electric field strength on the spacer surface gradually decreases and tends to be stable

from 2.7 kV/mm on the uncoated spacer surface to 1.1 kV/mm on the 20-wt% TiO2/epoxy-coated spacer. We hope that this study can provide guidance for the optimal design of DC GIL spacers under the electrothermal coupling field.