Measurement error which is caused by the position of reference ground point and strong electromagnetic interference is introduced in detail. Based on the results, reliable and effective methods for anti-interference, such as surge absorption circuit and floating measurement, were applied to measurement unit. As the results, in the impulse current system the measuring accuracy can be assured and the performance of electromagnetic compatibility can be enhanced. With voltage level continually increasing in power system, how to ensure power system security, reliability, and stability operation has become an un-ignored problem. Lightning interference is an important factor for maintaining normal operation of power system, because some power equipments may be damaged by lightning. So lightning protection also become indispensable in power system. Surge protection devices (SPD) are usually used to protect power equipments far from lightning damage, therefore its performance becomes crucial. The impulse current system mentioned below was a kind of special equipment designed to test SPD. The test results derived from the impulse current system will determine whether or not the SPD can meet the requirement of power system protection. According to lightning protection device characteristic, when it is applied an impulse voltage, it is equivalent to short- circuit as well as a very great impulse current will pass through it (this impulse current could be up to about several hundreds kA). In such condition as so great impulse current, measurement accuracy will be affected. Some questions, such as the position of reference ground point and the placement of measurement sensors including current shunt and voltage divider, will be considered to be crucial. If the questions mentioned above can not be considered seriously, an intolerable measurement error will be produced. In the other hand, companying with an very great impulse current flowing through the loop, a strong electromagnetic interference can be produced by the impulse current system itself; so strong impulse electromagnetic interference maybe disturb the system stability, either influencing measuring accuracy or damaging the system normal operation. For a standard and high performance impulse current system, there are many questions that are considerable. But in all questions, there are two important factors that have to be considered seriously, one is electromagnetic compatibility, and another is reliable measurement accuracy. It's significant for assuring system excellent performance(1). In this paper, we mainly analyze the reasons of making measurement error, and discuss the effects of the position about reference ground point and strong electromagnetic interference on measurement error. Based on the results, some effective means were used to reduce measurement error in the impulse current system. It is very significant for designing and manufacturing impulse current system.