Abstract:In order to reduce the measurement error of the lightning Grounding Resistance Tester. In this paper, take the 4102 Ground Resistance Tester for example,through analysing its measurement error,,find out the main factor of the influence of measurement error is a correspondence between relative distance of P electrode, C electrode and E electrode with ground network maximum size D;Meanwhile, according to the constant electric field theory, can calculate the correspondence between d12 with d13 under the condition of the measurement error is zero, according to the measurement principle of the potential drop, can deduce the mathematical expression of the measurement error, and then, draw out the graph of relationship between measurement error δ and d13/D.Within the allowable range of the measurement error, derived eventually the logical correspondence between d13 and ground network maximum size D; Thus, the paper provided the main ideas and methods of reducing the measurement error for testing personnel in using 4102 Ground Resistance Tester.