The invention provides a 500 KV double-post-insulator electrification water washing method. The method comprises the steps of arranging five hydraulic monitors around a 500 KV double-post-insulator and setting length of washing water columns of the hydraulic monitors to be not less than 5 m, wherein two hydraulic monitors are arranged around a small-post-insulator and the included angle between the two hydraulic monitors is 160 degrees, three hydraulic monitors are arranged around a big-post-insulator, two of the three hydraulic monitors and the two hydraulic monitors arranged around the small-post-insulator are side by side, and the include angle between each of the two of the three hydraulic monitors and a third hydraulic monitor is 100 degrees; and washing the small-post-insulator and the big-post-insulator with a method of synchronous washing with the five hydraulic monitors, wherein the washing is carried out with a method of one washing with three returning and uniform sweeping back. According to the 500 KV double-post-insulator electrification water washing method, the leakage current on the surface of the double-post-insulator is small during washing, probability of occurrence of pollution flashover is low, safety is high, filthy dead angles do not exist after the washing, washing is complete, and washing efficiency is high.