The invention provides a dielectric loss testing method and device of a 500kV current transformer. The dielectric loss testing method comprises the following steps of: adopting a shielding measure on a flexible connection part of a disconnecting switch of the 500kV current transformer and a flange of a disconnecting link knob insulator, and connecting the flexible connection part of the disconnecting switch and the flange of the disconnecting link knob insulator with a shielding end of a testing electrical bridge. The dielectric loss testing method disclosed by the invention has the advantages of greatly lightening the labor intensity of maintenance personnel on the premise of ensuring the testing reasonability, shortening the poweroff maintenance time, reducing the non-natural wear, saving a crane, reducing unsafe factors, saving the cost, having great practical benefits in terms of safety and economy and improving the detection accuracy at the same time.