This paper, from the principle of frequency sounding, illustrates that there are three field zones for frequency sounding of artificial source, far-field data of controlled-source audio-frequency magnetotellurics (CSAMT) were interpreted by audio-frequency magnetotellurics (AMT).  After data in near-field has been corrected, it is interpreted by AMT. Because near-field correction is based on homogeneous half-space mode, the correction error is bigger. Therefore, it is presented that data of ratio apparent resistivity without correction or data of single component of electromagnetic field are directly interpreted by inversion.