In response to the monitoring requirements for the operation status of high-voltage lightning arresters, the problems of weak anti-interference ability, low accuracy, and lack of full current monitoring of traditional online monitoring devices are solved. A technical scheme for online monitoring of lightning arrester operation status based on Tunnel Magnetoresistance Effect (TMR) current sensor has been proposed. This article is based on the TMR current sensing principle to complete the design of a complete online monitoring system for line lightning arresters, achieving high-precision measurement of lightning impulse current, leakage current and other full current waveforms of lightning arresters. The monitoring error of impulse current is within 1%, and the monitoring error of leakage current is within 0.5%.