In this paper,from theoretical calculation and practicaI observation data,we discussed a kind of yearly change which presents low vaIue in winter and high vaIue in summer at some earth resistivity stations in our country.lt is pointed out that there may be three kinds of reasons Ieading to such a yearIy change.Among them the principal one is the contrary con-tribution of resistivity variation in overIayer medium to observed apparent resistivity for some of special geoelectrical profiles,in which the variation of overlayer resistivity results in a non-linear variation of underground current density in a special geoelectrical profile.The overlayer response coefficient sishows the negtive,which is a very apparent mark for such a special geoelectrical Profile.In addition,the eliminating approach about thrs kind of yearly change is also discussed.