Abstract: The new type of IR drop measuring instruments which displays through computer and digital tube is superior to such metering devices made up of the conservative electrical instruments as the constant meter, double integral digital volmeter, etc., in such advantages as high precision, fast speed, being able to catch the transient potential value upon power-off, small size, light weight, portable in the field. It proves through measurement on LiuHe―YiZheng section that this is the more advanced instrument in the future impressed cathodic protection test, which shows that IR drop measured in this way with power-off at both Xu-Yi and Yi-Zheng pump stations indicates that the real ptentials of the pipeline are imvariably lower than the least potential while power is supplied only at Liu-He station. The result is satisfactory. But the real potential of the pipeline is getting a bit higher with power supplied at both Liu-He and Yi-Zheng pump stations at the same time, however, bigger role in protection is played at Yi-Zheng, with the most IR drop at the converge point at Liu-He and the least IR dsop at Yi-Zheng pump station,