The utility model discloses a lightning arrester with leakage current detection function, and overcomes the problem that detection of the leakage current of a conventional lightning arrester may be subjected to strong electromagnetic interference, the signals are difficult to extract without affecting and live-line monitoring is difficult to realize. The lightning arrester comprises an externally sealed umbrella cover and a core set arranged in the umbrella cover, wherein a first aluminum electrode is arranged on the upper portion of the core set and a leakage current measuring sensor is arranged on the lower portion. The leakage current measuring sensor comprises a second aluminum electrode, a third aluminum electrode and a resistance sheet, wherein the second aluminum electrode is provided with a detection anode P+ led out to the external of the umbrella cover, a detection cathode P- is led out of the bottom of the third aluminum electrode, and the resistance sheet employs a sampling resistor R and a protective valve block Z6, which are parallelly connected. The lightning arrester integrates with a leakage current measuring sensor, and is connected with a measuring instrument through extraction electrodes. Live-line monitoring of the lightning arrester is achieved without affecting the lightning protection effect of the lightning arrester body.