The invention discloses a lightning arrestor online monitoring device with a shielding function. A signal acquisition device adopts a straight-through current transformer to measure a total current signal which flows through a grounding wire of a zinc oxide lightning arrestor, and uses a voltage acquisition module to obtain system operating voltage at the position of a secondary terminal of a voltage transformer which is connected in parallel with the zinc oxide lightning arrestor. The lightning arrestor online monitoring device with the shielding function is characterized in that a lightning arrestor surface leakage current shielding coil is arranged, the lightning arrestor surface leakage current shielding coil is wound and fixed on the upper surface of a cluster parachute at the bottommost layer of the zinc oxide lightning arrestor, the lower end of the lightning arrestor surface leakage current shielding coil and the grounding wire of the zinc oxide lightning arrestor at the lower part of the straight-through current transformer are jointly grounded. The lightning arrestor online monitoring device with the shielding function can guarantee that the leakage current and the resistive current of the lightning arrestor can be accurately measured under various weather conditions.