Abstract: The paper, from the principle of frequency souding, ilustrates that there are three field zones for frequency souding of artificil source, far-field data of controlled-source audio-frequency magnetotellurics (CSAMT) were interpreted by audio-frequency magnetotellurics (AMT). After data in near-fied has ben corrected, it is interpreted by AMT. Because near-field conrrection is based on homogeneous half-space mode,so correction error is bigger. Therefor,it is presented that data of ratio apparent risistivity without correction or data of single component of electromagnetic field are directly interpreted by inversion.