Abstract: The measurement of pipeline to ground potential is the most common method to evaluate protection condition of buried and coated metal pipelines, the common method to measure pipeline to ground potential always covers an IR drop, it is hard to judge the cathodic protection condition of pipeline according to the data obtained. The IR drop in measurement of pipeline-ground potential must be eliminated. An equivalent circuit is taken in the paper to analyze the production of IR drop and the effect, to eliminate IR drop the principle of the transient power loss method and probe method and application limits are presented, the multifunction probe for cathodic protection is recommended.