Currently, there is little experience about design of the 1-tower-double-circuit DC transmission lines. But the electromagnetic field distribution under its lines is complicated. In order to study the nominal electric field distribution of 1-tower-double-circuit DC transmission lines under different situations and a variety of operating conditions, the currents with analytical solutions are used to simulate the discrete or uneven distributed continuous charge. In the works within an acceptable range, the linear equations are built to solve simulation charge according to the electromagnetic theory. And ground nominal electric field of 1-tower-double-circuit DC transmission lines is calculated. The nominal electric field distribution extreme value extreme under different arrangements and nominal electric field distribution under a variety of operating conditions are analyzed comparatively. In this paper, the results show that the arrangements of lines have effects on the distribution characteristics of nominal electric field in normal condition. When monopole or bipolar or the bipolar of one line doesnt work, the change of nominal electric field is pronounced, but their extremes reduce.