Abstract: A large temperature gradient may be generated inside and outside the core of high-voltage DC dry-type bushing due to the heat generated by the core during operation, thus a phenomenon of the electric field flipping occurs, making the field strength at the outermost pole plate far greater than the design field strength of the insulating structure. To this end, the ±800 kV converter transformer dry bushing is taken as the research object, the commonly used cone model of the capacitor core is used, and the multiphysics coupling software is used to solve the temperature field and electric field distribution. Through the analysis of the simulation results, an optimized design scheme for the capacitor core is proposed. By reducing the design electric field strength of the insulating structure at the outermost electrode plate, the electric field strength at the outermost electrode plate under the temperature gradient is reduced. The study shows that the decrease of the pole plate length in the radial direction in the cone model will result in the gradual increase in the radial size of the electric field flip under the temperature gradient. The electric field gradient shows a linear increase trend in the radial direction. As the temperature gradient increases, the electric field gradient increases to a certain extent everywhere in the radial direction, and the increase degree is similar, showing that the electric field gradient distribution curve shifts upward as a whole.By adjusting the design parameters of the capacitor core.such as the ratio of the radius of the outermost plate to the innermost plate ξ_r, and the inverse ratio of the length of the plate ξ_l, and by appropriately increasing ξ_r /ξ_l, the electric field strength at the outermost plate can be reduced under no-load, thereby reducing the maximum field strength appearing at the outermost plate under the temperature gradient.When ξ_r and ξ_l are 4.8 and 3.6, respectively, the volume of the capacitor core is the smallest, and the maximum electric field at a current carrying capacity of 5 kA is 4.58 kV/mm.