Abstract: Electrical characteristics of SRD(step recovery diode) are analyzed,and a model of SRD is proposed.SRD is here looked as the parallel connection of nonlinear resistance and a nonlinear capacitance.In order to acquire a curve of the nonlinear resistance and capacitance,several discrete values of the nonlinear resistance and capacitance are measured.Then the nonlinear resistance and capacitance vs voltage are fitted by polynomials in several segments.The impulse production circuit is simulated based on this model.The circuit is achieved.The measured width of the pulse is 200?ps and the measured magnitude 3.3?V,which coincides with the simulation result,and the model is thus verified.