The central-loop device is an important surveying means for transient electromagneticmethod. It is necessary to make a rapid interpretation and improve the interpretation level. The electromagnetic field stimulated by the central-loop-source in the late period is similar to the plane-electromagnetic-wave. Through the time-frequency conversion, the TEM data are transformed to the plane-wave field data, thus constructing the system of M×N order underdetermined equations related to the reflection function. The authors have designed a computer programme to solve the reflected function sequence q_m with the method of Linear programming, and the error between the inversion result of a host of models and the theoretical value is very small, which indicates this method is feasible and the calculation result is correct. The electromagnetic response time-section is drawn with the parameter q_m, which realizes the explanation of the TEM rapid imaging. The imaging section clearly reflects the geoelectric characteristics of the section. The processing results of the field data demonstrate that this method is useful and practical.