Abstract: With the constant construction of UHV power grid, the available transmission corridors for planning UHV transmission lines is limited. To improve the efficiency of existing transmission corridors, it is necessary to research the transmission technology for ±800 kV double-circuit transmission lines on the same tower. An analysis is made on the insulation coordination of converter station and transmission line. In converter station, the adopted insulation level is same as the conventional one. For the ±800 kV double-circuit transmission lines on the same tower, the line parameters may vary due to the effect of the mutual inductance between lines, which could influence the overvoltage level. The suspension mode of V-shaped insulator string adopted in the ±800 kV double-circuit transmission lines is extremely different from the one adopted in the ±800 kV single-circuit transmission lines. Based on the researched results of overvoltage and the discharge characteristics experiment of the real tower in the project of double-circuit transmission lines, the insulation coordination has been investigated. For the ±800 kV double-circuit transmission lines, the minimum air gap is recommended.