The invention discloses a method and a system for optimal phase sequence determination of four-circuit transmission line on that same tower. The method comprises the following steps: a calculation model of a power frequency electric field of the four-circuit transmission line with the same tower is established; when the maximum electric field intensity is less than a first predetermined value, theheight of a conductor to ground is obtained; and the lowest height of the conductor is determined. The calculation model of audible noise is established. Based on the calculation model of the lowestheight of the conductor and the audible noise, the audible noise values at the evaluation points under all possible phase sequence arrangements are calculated by the exhaustive method. The calculationmodel calculates the distribution of the audible noise value, and eliminates the phase sequence arrangement mode of the asymmetric distribution of the audible noise value on both sides of the conductor center. A smaller noise value corresponding to a smaller one of the audible noise values is obtained according to a predetermined number in the selected phase sequence arrangement mode. A phase sequence arrangement of a region width having an electric field strength greater than a second predetermined value is calcuated. A phase sequence arrangement corresponding to the smallest noise value corresponding to the audible noise value and the smallest region width corresponding to the electric field strength greater than the second predetermined value is selected.