Abstract: In this paper, the very complex natur of the normal variation of earth resistivity and its possible causes are discussed on the basis of a variable geoelectrical resistivity profile model for the station site.Numerical computations give a qualitative and quantitative relation between the normal annual variation of earth resistivity and the parameters of the geoelectrical profile at the station site. Such a relation indicates the influences and controlling effect of the parameters of the geoelectrical profile on earth resistivity.By comparison with the results of actual observations at some earth resistivity station sites, the above conclusions have been verified. They show the possibility of obtaining steady normal variations of earth resistivity and the methods concerned.