Abstract: In China, there were many reports relative to the cathodic protection which more frequently discussed the IR drop in pipe-to-soil potential measurements than other factors.It is demonstrated IR drop is only one of the sources of error, It is important for operator to master the measuring techniques, do intense resarch for eliminating IR drop.A hint is given the objective of which is to identify the sources of error and minimize errors. In addition, working techniques for measuring procedure is given t0 minimize errors.