The effect of rear low-pass filter on electric energy metering has been analyzed quantitatively according to the principle of active power metering. The theoretical analysis results show that the rear low-pass filter of the electric energy meter has no effect to the measurement of voltage and current waveforms periodic, while metering inaccuracy coming out for voltage and current aperiodic waveforms produced by impact load. Taking the electric arc furnace load as an example, a simulation model to study electric energy metering for the impact loads has been built. The simulation results show that the rear low-pass filter of electronic energy meter will increase electric energy metering error for the impact load.