The correlation identification mymargin (CI) algorithm can obtain underground electrical information from electromagnetic data using pseudorandom current. The precision of identification would be limited by truncation error, because the CI algorithm has the limitation of the maximum identifiable range in the numerical calculation process. To solve this problem, the identification results are extended by exponential extrapolation (EE) algorithm, and correct the truncation error by subtracting the response of extrapolated data in electromagnetic data. The simulation test shows that the maximum relative error of identification results and electromagnetic impulse response of the Earth decreased from 97% to 37% through the CI–EE method. In the field test, the inversion results of the CI–EE method found aquifer, which is agreed with the other projects for the statistics of electrical parameters of main strata in Alxa area.