The level of lighting trip on transmission lines is affected by the quality of grounding device directly

therefore accurate measurement on grounding resistance of tower is very important.The principle of grounding resistance measurement is analyzed and the linear three-pole method which is applied in engineering frequently is presented in this paper.The factors affecting the accurate measurement is studied and corresponding measures are given.Case studies demonstrate that key factors ensuring accurate measurement are whether the zero potential reference point is selected correctly or not and the judgment on the measurement results.And the measurement accuracy is improved by the linear three-pole method based on GPS effectively.