对1 000 kV锡盟—南京特高压输电线路的锡盟—北京东段，利用电磁暂态分析程序(ATP-EMTP)计算了单回和同塔双回混合线路的电气不平衡度以及最佳换位点位置。计算结果表明，对于锡盟—北京东段单双回路混合线路，最佳换位点不在沿线路长度的1/3和2/3处。从电气不平衡度的角度推荐在单回路段进行1次全换位，双回段逆向序排列不换位，2基换位塔分别位于63.14和103.13 km处。

For the Ximeng-Beijing east section of 1 000 kV Ximeng-Nanjing ultra high voltage transmission line, this paper calculated the electric unbalance degree and best transposition position of the mixed transmission line with single-circuit and double-circuit on same tower based on ATP-EMTP. The results shows that the best transposition point is not the 1/3 or 2/3 equal position of lines. Basing on electric unbalance degree, this paper recommends that the lines has a full transposition in single-circuit sections without transposition in double-circuit sections with negative phase sequence, and two transposition towers are located at 63.14 and 103.13 km.