Abstract: By forward modeling of homogeneous and horizontal 2-layered medium and surveying example,some exchange property of the CSAMT appavent iesistivity value from far-field to near-field has been uiscribed in the paper.And the detali explanation abovt the corre; pondence relation between pEx and the 4-rodsymmetrical electric sounding (Schlumberger) apparent resistivity ps has been made. It is of significance for the interpratation of the pEx curve.