The field distribution on the ground near the transmission line is an important index to evaluate the electromagnetic environment.In this paper

the validity of the semi-experiential formulas to calculate the total electric field and the ion current density is testified.The influencing factors of the field distribution under the ultra-HVDC line are analyzed.It can be seen that the variation rules of the total electric field and the ion current density are quite different from that of the nominal electric field.The nominal electric field is greatly influenced by the height of conductors.However

the total electric field and the ion current density only greatly are not influenced by the height of conductors

but influenced by the diameter and the number of the sub-conductors.