For the advantage of Stable signal and large detective depth of the Time Domain Electromagnetic Sounding, it is widely used currently for Mineral and Geological Structure Exploration. But in general, it is supposed some extremely conditions for processing and explaining the observed results. And it is very difficultly to fit that conditions we supposed. So we cannot get the exact processing and explaining of the observed results. We suggested a method by using Numerical Differential Calculating to obtain the apparent resistivity of TEM sounding in this paper. It can get the results close to the real Geo-Electrical section. We can simplify the explanations of the observed results. And we can get the Model Parameters for the inverse calculating easily. http://www.j-es.org/paperInfo.aspx?ID=1049
