The fall of potential method is generally used for measuring the earthling resistance. This method needs two auxiliary electrodes and it is required that two auxiliary electrodes are placed at enough distances from the earthling electrode，e. g. building foundation. However， in urban area there is not enough space for taking measurement. So，it is very difficult to measure the earth resistance precisely. However，there is the 4-potential method when it stand on the theory of the fall of potential method. It is purposed of this paper to basic study on correction method of measured earthling resistance by 4-potential method.