Nonlinear characteristics of SRD are analyzed. A model of SRD for simulation is proposed based on dynamic capacitor and pn diode, which can be used in ADS software. A method of producing UWB monocycle short pulse based on SRD and Schottky diode is proposed and analyzed theoretically. The UWB signal generation produces monocycle pulse with the width of 400ps and the p-p amplitude of 15V. The simulated result meets the tested result, which proves the veracity of the new model of SRD.