This paper describes the theoretical basis and monitoring indices of applying resistivity technique to the prevention of seawater encroachment in Laizhou Bay area,Shandong Province,and analyses the variation regularity of stratigraphic resistivity in seawater and salt water encroachment area,the determination of the interface between salt water and fresh water,and the delineation of the seawater encroachement channel as well as the detection of migration regularity of the interface.