Abstract: This paper introduces a case of using live detection technology to find the defects of 110 kV metal oxide arrester and successfully handle them. Through the test, disassembly and fault diagnosis analysis after applying for power failure, it is concluded that the direct reason is that the moisture entering from the top caused by the inadequate compression of the sealing ring in the lightning arrester assembly link is the damp of the internal valve plate, which verifies the effectiveness of the live detection technology.