The utility model discloses a 500kV zinc-oxide lightning-arrester dc tester which is characterized by comprising a lightning arrester (1), an insulating pedestal and a foldable testing support. The lightning arrestor is fixedly connected to the center of the insulating pedestal, and the insulating pedestal is detachably connected with the testing support. Compared with the prior art, the 500kV zinc-oxide lightning-arrester dc tester is simple in structure and strong in operability, can accurately measure the U1mA of a second section of the lightning arrester needless of dismounting a lead, decreases the frequency of high-altitude wiring, and reduces the risk of workers. The total height, which is 150cm, of a supporting unit is the same with the height of a dc high voltage generator, so that the grounding capacitance and current can be effectively reduced, and the testing accuracy is ensured. The tester is also characterized by being easy to mount and dismount and convenient to carry, and can effectively improve the working efficiency.