When studying the surface charge accumulation and dissipation law of insulating materials under HVDC transmission lines，the charge density can only be calculated by surface electrostatic potential inversion of insulating materials. However it is difficult to accurately calculate the surface charge density when the insulating material surface is curved. In this paper，a charge density inversion method for curved surface was proposed. The potential measurement points were selected reasonably and intensively，and then curved surface was divided into triangular meshes according to the selected measurement points. The normal vectors at each point were obtained，and the surface charge density was then inverted. As an example，the surface potential of 3D printed curved surface and suspended insulator was measured，and the surface charge density was calculated. The calculated results are in accordance with the theoretical analysis trend. The electrostatic potential of insulating material surface has a strong correlation with the charge density，and the charge density corresponding to the high potential area is also large. The charge density presents a“concentric circle” distribution according to the distance from the discharge electrode，but the charge near the suspended insulator cap is difficult to accumulate，and the charge density is small.