The utility model discloses a leakage current of an arrester compensating system under electric power site environment, include: current sensor, operational amplifier, current output unit and direct current suppression unit, current sensor for measure arrester power frequency and harmonic leakage current, wherein current sensor is wide band open type punching current transformer, operational amplifier for output current to current sensor goes on enlargeing in real time, the current output unit for convert operational amplifier's output voltage into electric current through fourth resistance, export current sensor to, the direct current restraines the unit, and is parallelly connected with operational amplifier for the direct current output weight that restraines operational amplifier. The utility model has the advantages of through measuring arrester output current and the real -time offset current who pours into into rather than the size equals, the phase place is opposite for the work magnetic flow convergence in examination article current measurement return circuit is in zero, thus the interference of elimination arrester background leakage current to check -up work.