Abstract: EHV/UHV power transmission is the core technology to realize the global energy interconnection. As the most widely used conductor materials in power transmission system, the corrosion resistance of copper and copper alloys has been paid more attention. In the process of EHV/UHV DC transmission, there is a large magnetic field in the surrounding environment, which leads to the service environment of the copper components different from that of the ordinary transmission environment. The electrochemical corrosion behavior of the pure copper under the EHV/UHV environment was studied by potential polarization, electrochemical impedance spectroscopy, and element analysis in this paper. The results show that, the limiting diffusion current of the pure copper in 3.5% NaCl solution (mass fraction) under the UHV/UHV environment is larger than that without magnetic field, and the reaction resistance without magnetic field is significantly increased compared with that under 0.1 T magnetic. Combined with the results of electrochemical impedance spectroscopy, X-ray diffraction, and elemental analysis, it is shown that the high-intensity magnetic field (0.1 T) can reduce the corrosion resistance of the pure copper, and the main corrosion product is Cu₂O.