According to control indexes for DC transmission line, such as the composite electric field under the wires, ion current density of the ground, field intensity induced by radio interference and corona audible noise et al, the corresponding calculations are carried out for various bundle conductors of DC transmission line in 3 000~5 300 m ultra-high altitude regions. It is concluded that 4×LGJ-400/35 aluminium conductor steel reinforced (ACSR) is applicable for ±400 kV DC transmission line in ultra-high altitude region.