Abstract: With the development of the wide-field electromagnetic method, the scope of data collection has been gradually expanded. To avoid the none-far-field resistivity distortion, this paper proposes a definition method suitable for the full-field apparent resistivity of the controlled-source electromagnetic method based on the inverse function principle. With this method, the full-field apparent resistivity can be calculated using a single component or multiple components. The full-field apparent resistivity of a homogeneous half-space model and a layered model was calculated using individual components of electric and magnetic fields and their ratios. The results show that the definition method proposed in this paper can achieve the definition of frequency-domain apparent resistivity that is not limited by space and thus can better reflect the resistivity distribution of underground media.