Abstract: Power frequency phase parameters of transmission lines are essential parameters of overvoltage calculation, so it is necessary to obtain the phase parameters of 1 000 k V AC double-circuit transmission lines on the same tower before the lines are put into operation. Phase parameters of short distance lines can be accurately obtained by measurement and calcalation without taking into consideration their distributed parameter characteristic, while errors tend to arise for long distance lines. In order to get accurate phase parameters of long distance UHV transmission lines, a multiconductor transmission line was modeled and analyzed by π lumped parameter and distributed parameter equivalent circuit respectively in this paper. A method was proposed to obtain mutual capacitances between phase conductors by measuring the voltages or currents at both ends of each phase conductor and calculating mutual admittances equations between phase conductors. Equations of mutual impedances between conductors were deduced based on the distributed parameter characteristic of lines. Self-parameters of phase conductors were calculated according to the relationship equations between the voltages and currents on both sides of phase conductors. The results indicate that calculation errors of the parameters can be reduced by adopting the methods, which has been verified by means of simulation. The methods were used to obtain the phase parameters of 1000 k V Huainan-WuhuⅠ and Ⅱ lines of eastward transmission of Anhui electricpower and can provide exact data for overvoltage calculation of the project.