As the rated voltage of the transmission line increases, the electromagnetic environment of ultra-high voltage transmission lines has become one of the main factors to determine the tower size. The comparison of the electromagnetic environment is analyzed between the 1 000 kV three-phase double-circuited transmission line and the six-phased 578 kV. The numerical results show that the electromagnetic environment of a six-phased transmission line is much improved with the same tower configuration and nominal tower height. Further more, the characteristic of the electromagnetic environment of a six-phased transmission line with respect to the nominal tower height is studied in detail. With the decrease of nominal height, the electric field strength on the surface of the ground wire and the two highest transmission lines decreases, while that of the other conductors increases. The ground-level electric field, radio interference and audible noise increases as the nominal height decreases. In comparison with a three-phased transmission line with the same phase voltage, the electric intensity on the surface of the conductor of the six-phased transmssion line is much lower than that of the three-phased ones. The six-phased technology of the transmission line can essentially improve the electromagnetic environment of the high-voltage AC transmission lines.