At present, it is required that the polarity distance of ±800 kV UHV DC transmission lines constructed or constructing is not less than 22 m in our country. In this paper, the possibility of decreasing the polarity distance is discussed by considering electromagnetic environment, length of the composite insulator string, air gap, angle of the V style insulator string and so on. In addition, the economic benefits are analyzed. The results obtained provide references for the design of future UHVDC transmission line.