On the basis of analyzing theoretically the feasibility of detecting fresh-salt water interface of coast aquifer composed of multilayered geologic structure by electricity detection,this paper surveyed some areas near the Pacific Ocean coast.It surveyed the wells near and far away from the coast by the parallel methods of electricity detection and surveying vertical conductivity of well water.The results showed that the fresh-salt water interface depth detected was nearly coincident with the upper layer of mixed area divided according to well water conductivity,i.e.the position of fresh-salt water interface detected is on the upper layer of mixed area.So electricity detection is an appropriate method to monitor seawater invasion and also a simple,fast,cost inexpensive detecting technique in determining fresh-salt water interface depth compared with traditional techniques.