The encoded source electromagnetic sounding method based on circular correlation identification and the calculation method of whole zone apparent resistivity are put forward. Using the inverse repeated M sequence as the excitation signal, the encoded current from the source is through the grounded electrodes of horizontal electric dipole, the electric field with the same horizontal direction of the transmitter dipole or the vertical magnetic field is measured in the equatorial array. The

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... ion current and the received electric voltage signal or the vertical magnetic field are simultaneously recorded in the time series at the sampling rate using the same acquisition equipment, and using circular cross-correlation method to obtain the earth frequency response, then the whole zone apparent resistivity spectrum are calculated according to the frequency response and measurement parameters of the electromagnetic sounding array. The results show that the encoded source electromagnetic sounding based on circular cross-correlation method to obtain the whole zone apparent resistivity spectrum, raises the efficiency of electromagnetic sounding and improve the whole zone apparent resistivity frequency resolution, and due to the adoption of the circular cross-correlation method and the current signal of inverse repeated M sequence is an even multiple of power frequency, can effectively suppress the power frequency interference, so this method has enhanced anti-jamming ability.