Integrator is an important part of Rogowski coil electronic current transformer, but the accuracy of integrator is influenced by the DC error caused by amplification sampling analog circuits. This article analyze some methods which are usually used in eliminating DC error and put forward a mirroring method which means to sample a pair of mirroring analog signal by a pair of the same ADCs. The simulation and hardware test result shows that during the measurement of secondary harmonic and transient current , only the DC error is eliminated and the signal which is to be integrated is mostly left complete. As a result, a higher integration accuracy is reached.