Abstract: This paper points out the advantages that the apparent longitudinal conductance is used to analyse the transient electromagnetic sounding data.On the other hand, for the sake of advancing the ability of distinguishing the electric layers, the road test data are processed adopting numerical means on the base of having ascertained the physical meanings of conductance and its differential curves, by this means we realize the differential coefficient imaging of the longitudinal conductance.Practices have proved that the results adopting this method tally with other inversion results very well, its "electricity event" clearly displayes the distributing configuration of the electric interface by via of the direct and visual feature.