The vertical component of magnetic field can describe inhomogeneity of median. Induction arrow that describes the relation between Hz and ( Hx, Hy ) migh t be t he best parameter for studying the horizontal inhomogeneity of electrical conduc tion. It has smaller distortion and better ability for avoiding electric noise. Direction of real arrow represents point away from the good conductor and the m agnitude of real arrow represents the difference of media with the surroundings at the depth. The application of induction arrow indicated that there might be some low resistivity bodies from surface to depth in Changbai volcanic area. The shallow bodies might be related to the geothermal resource and water in Tia nchi. The deep body may be correspondent to magma chamber.