In order to improve the safety and reliability of external insulation for ± 1 100 kV UHV DC converter station, this paper studied several key technologies of post insulator for ±1 100 kV UHV DC, such as air gap external insulation, pollution, mechanical strength and so on. According to the technical parameters of ±1 100 kV UHV DC post insulator, the solution for those technical problems was proposed, combined with the design of ±800 kV UHV DC post insulator. The results could provide design basis for ±1 100 kV UHV DC post insulator, and technical support for the project construction and operation.