The DC grounding system is one of important parts in DC transmission system. In order to ensure the reliable operation of DC transmission systems, it is necessary to develop live working tools for UHV grounding systems. In this paper, the overvoltage of grounding faults on BP and GR modes is calculated firstly and the maximum amplitude is 288 kV. Then, the switching impulse flashover tests are carried out in live working air gaps of a simulation tower. The routine method is employed and the live working safety distance is calculated as 0.65m. In addition, for the electric field strength at the surface of live working workers is generally less than 240 kV/m, the additional protection is not required for such electric field. Nevertheless, thermal insulation measures should be adopted due to the influence of hightemperature wire on the operating personnel and insulation tools. It is recommended to use the insulated rod operation method. Otherwise, necessary measures should be taken to ensure the safety distance when the direct work method is selected.