In this paper

the standard current of lightning subsequent return-stroke is splited into a breakdown current and a corona current based on IEC1312-1.The breakdown current and the corona current are represented by a new pulse function and a double exponential function respectively.The subsequent return stroke standard current is fitted and some parameters are obtained.We assume for the electromagnetic fields calculating of lightning subsequent return-stroke a breakdown discharge time constant and a corona discharge time constant based on DU model.The characteristic features of calculated field waveforms are similar to those of the typical field waveforms.