Abstract: Model of stepped leader current is the basis of lightning movement simulation and strike analysis, and it is indispensable for lightning protection design, theoretical research of shielding failure for transmission lines, etc.. Physical model of stepped leader was given, which includes a main channel and a tip. Current model of stepped leader was also given, which well simulates the stepwise propagation of lightening and charge change properties of stepped leader-s tip. Electric field on the ground level produced by stepped leader was derived and calculated by charge simulation method and dipole technique, and its simulation results show that the average electric field peaks and time interval between stepped leader pulses of far-zone field agree well with the measured data. The close fields under different return strike current peaks also agree with the measurements of triggered-lightning.