The electromagnetic environment of 750 kV compact power transmission lines is not friendly due to its high voltage,short phase distance and high altitude.Generally speaking,as a result of the interaction of sub-conductors,the electric-field distribution on surfaces of sub-conductors equally arranged at circumference is nonuniform.The heterogeneity increases the electric field intensity on maximum surface of phase conductor,so that the radio interference and audible noise of the transmission line are increased.Therefore,the electromagnetic environment is improved by changing the arrangement of sub-conductors.The influences of optimized sub-conductors arrangement on the electric parameters of the transmission line are also discussed.The results obtained will provide references to the construction of UHV compact power transmission lines in our country.