Abstract: Firstly the transient electromagnetic(TEM) field convolution was given, and change rate of turn-off current is taken as a impact function, the field component of vertical step pulse excitation as the input signal. The convolution result is TEM response of arbitrary shape turn-off current. The current excitation pulse is regarded as a superposition of many vertical step function. The transient electromagnetic response of arbitrary current pulse excitation is induced by the superposition of step function response. When the measured value of TEM field and the turn-off current form are known, whole-stage apparent resistivity can be calculated by the method of programming. The paper gives two examples on TEM vertical magnetic field of slope turn-off current excitation of electric dipole source, a response of uniform half-space and all-time apparent resistivity, a response to the three K-type geoelectric section and whole-stage apparent resistivity.