The electric field distribution of UHV AC parallel lines have great influence on enviormental protection, the corridor width and the demolition range. the power-frequency electric field strength of 500～1 000 kV single-circuit and double-circuit AC lines under various conditions, such as different phase sequence, line heights and distances are studied in this paper, and then the distribution rule of electric field in 1 000 kV UHV AC parallel lines is obtained. Finally, the phase arrangement and the corresponding line space are proposed on the basis of the existing environmental standards, which could provide support for the construction and operation of UHV AC power transmission projects.