The invention relates to a method and device for flushing a 500kV post insulator with charged water. The method comprises the following steps of: when the 500kV post insulator is flushed with charged water, pressurizing de-ionized water via a high pressure water pump, transmitting the pressurized de-ionized water into a high pressure water gun via a high pressure water tube, opening a high pressure water valve on the high pressure water gun, laying out the positions of four flushing workers with water guns in hands according to charged water flushing water gun positions of four water guns of the 500kV post insulator, and safely flushing dirt on the surface of the 500kV post insulator based on a one-flush three-return charged water flushing procedure of the four water guns of the 500kV post insulator or a two-section even charged water flushing procedure of the four water guns of the 500kV post insulator to reduce the dirt to a safe level. The method and device disclosed by the invention have the advantages of no need of power-cut cleaning, benefit for the stability of an electric power system, convenience and safety for on-site flushing, no dead flushing space, capability of preventing electric devices from causing flashover and the like.