Standard current transformer is verified via current comparator. Otherwise, manual zeroing for current comparator is the key to limit verifying speed of standard current transformer. The research of electronic zeroing technique for current comparator is therefore of great importance. The development of electronic balancing device for current comparator is dedicated in the work. The electronic load for auxiliary CT is proposed based on voltage-controlled voltage sources. And in order to increase the speed and accuracy of balancing current comparator, adaptive zeroing technique is presented, in which variable step methodology is employed. At the same time, the programmed amplification technology is applied into real-time monitoring the wide-range signal of zero winding in current comparator. Besides the comparison tests of manual and automatic balancing current transformer have been designed. And the proposed instrument has been proved that its performance meets the requirement of standard CT verification based on current comparator.