Electronic Transformers(ETs)are the most impartment equipments of the Smart Grid. But there are many optics and electronics devices used in the ETs, and usually word under the high voltage part or low voltage part of primary equipments, so the ETs are easy interfering by the complex electromagnetic environment. This article aims to improve the measurement accuracy of the Electronic Voltage Transformer (EVT) during the surge test, find out the root cause and put forward two solutions. One solution is for the output of the power and the other is for the input of the power. We have finished the theoretical analysis and experimental verification, and prove there are worked to improve the reliability of the EVT.