Abstract: With a three-layer resistivity model, calculation has been made in this paper of the variation of apparent resistivity due to change of resistivity profile parameters. It can be shown that the variation of apparent resistivity caused, by the change of the ground water level may be estimated.With this result one can determine the amplitude of the anomalies of apparent resistivity caused toy change of ground water level, thus facilitating qualitative or quantitatively analysis of the relation between resistivity variations and the occurrence of earthquakes. It has been found that the variation of apparent resistivity is very complicated. There are many factors which, may cause variations of apparent resistivity, but water is a very important disturbing aqent. Therefore, it is perhaps of great significance to study this ploblem.