In this paper, Wide Field Electromagnetic Method is established as a new electromagnetic exploration
method. The WFEM apparent resistivity is defined from the complete analytical expressions of the horizontal
electrical field source and the vertical magnetic field source on the surface of a homogeneous half space. In the
definition, there is no limit in the distance between the observation points and transmitting source, while in
CSAMT “Cagniard resistivity” is only valid in “far zone”. In CSAMT, two orthogonal electric and magnetic field
components are needed to calculate the resistivity. However, only one component is needed in WFEM.
Another character of WFEM is its signal type. A kind of signal called 2n sequence pseudo-random
multi-frequencies signal is adopted in this method. Signal’s transmitting wave not only takes on the characteristic
of certain random wave, but also can be set in advance and created repeatedly. Its signal amplitudes of the main
frequencies are nearly, the amplitudes won’t be weakened as the frequency increases. The interval between the
adjoining main frequencies is even and reasonable in logarithmical coordinate. The application of the 2n sequence
pseudo-random signals shows the ability to improve the energy utilization and working efficiency.