The invention provides a lightning arrester discharging current monitoring system and method. The system comprises a hollow wire coil, a passive integrator, an integrated electro-optical modulator, a light source, a first optical fiber, a second optical fiber, an optical detector and a collecting device, wherein the hollow wire coil and the passive integrator are used for subjecting lightning arrester discharging currents to passive measurement, the integrated electro-optical modulator is used for converting detected electric signals into optical signals, and the optical detector and the collecting device in a control room end are used for converting received optical signals into electric signals and recording the electric signals. A problem that electricity supply of a lightning arrester end can be easily affected by circuit damaged caused by ground potential rise is solved, a problem that signal transmission is susceptible to interference is solved, and the lightning arrester end can be safely and effectively insulated from a control room.