The invention belongs to the technical field of on-line detection on the insulation state of an arrester, relates to a device and a method for on-line inspection on the insulation state of a zinc oxide arrester, and in particular relates to a device and a new method for performing on-line inspection on the insulation state of a gapless metal zinc oxide arrester. A host case of the device provided by the invention employs a CPCI (Compact Peripheral Component Interconnect) type structure; a measurement connecting cable, a signal conditioning circuit, a data acquiring and processing circuit and an industrial control computer are arranged in the host case; all of the circuits are connected one another through a bottom-end connecting circuit board; and a touch display screen is arranged on the host case. The device provided by the invention is capable of accurately and stably measuring the resistive current of the arrester without leading out a secondary signal of a voltage transformer, thereby effectively obtaining the state of the arrester under the operating voltage and guaranteeing safe and stable operation of the equipment.