Second order linear system has been adopted to describe the property ofthe simple-shaped polarized body in homogeneous electric field. The responseto the order-leap signal by this earth current cross section is a linear combin-ation of two exponential functions. StudiesreveaJthe following facts.- two timeconstants of the system are only related to geophysical parameters and areinvariable with respect-to the whole observation profile? the coefficients ofthe two exponential functions are connected not only with geophysical para-meters but also with geometric factors; the value and sign of the two coeffi-cients are variable at different survey points in the profile. Consequently,eight different types of discharge curves might exist. The effect of continuouscharging interval on discharge curve has also been examined. Theoretical calcu-lations may well be used to explain field suiveyed data and model test resultsprovided by such previous workers as J. Bertin, J. loeb and Fu Liangkui andmay indicate some existing phenomena which remain undiscovered. The authorholds the opinion that the theoretical research method adopted in this papermight find application in more complicated circumstances.