The method of ultra-high frequency is widely used for the PD online monitoring of electrical equipments, which requires a waveform generator of high stability and reliability to simulate UHF signals when it comes to the location and quantitative analysis of those signals. In order to satisfy this need, we design a nanosecond pulse source based on digital circuits and its signal is able to imitate the real UHF signals of PD. In this paper, we analyze the principle of how to take advantage of digital circuits to create steep pulses specifically and employ virtual instrument to produce square wave signals with variable frequency and amplitude as trigger signals of pulse origins. Besides, Pspice is used to simulate the pulse response characteristics of gate circuits and we establish experimental platform to test its performance. And just as the experimental results show, this pulse origin can generate a type of steep pulse, whose magnitude is up to 2V, repetition rate ranges from 50KHZ to 20MHZ, rising time is 1ns and pulse width is 3ns, and we carry out relative PD experiments by it and find such pulse is able to simulate UHF signals of PD effectively.