DC disconnector is one of the key equipment in valve hall, consisting of hoop, fixed contact, moving contact, folding mechanism, post insulator, pedestal and shielding ring. Because of the complex structure of disconnector, severe electric distortion was likely to occur in this part. Thus analysing the potential and electric field distribution of the equipment was necessary. In this paper, a model of a one-column-vertical telescopic disconnector in ±500kV valve hall was established and calculated using finite-element method software COMSOL. The surface electric field of the opening and closing disconnector was calculated separately and compared with the critical value of the electric field (20kV/cm). According to the calculation results, the structure parameters of disconnector were adjusted in some aspects. After the optimization, the maximum surface field strength in closing condition appearing at the bottom of pedestal was 18.5kV/cm and the maximum surface field strength in opening condition appearing at the shielding ring of hoops was 19.2kV/cm. The calculation results could provide valuable references for the design of DC disconnector in ±500kV valve hall.