Abstract: The magnetic switch is used widely in the field of pulsed power technology due to its special saturation conduction mechanism, and it can be used as a pry off switch to steepen the falling edge. A high-voltage pulse quasi square wave with a certain flat top can be obtained on load based on the voltage clamping effect of metal-oxide varistor, which enables the adjustment of the pulse width by changing the volt-second integration of the magnetic switch. This paper presents a high voltage pulse generator with adjustable pulse width. With the use of varistor to generate high-voltage pulse quasi-square wave, and the magnetic switch as a pry off switch to steep the falling edge, by changing the magnetic switch reset current to control the reset depth of magnetic switch, it achieves adjustable pulse width. This paper presents theoretical analysis as well as simulation research and the preliminary experimental research based on the simulation result. In the preliminary experiment, the falling edge of the voltage waveform obtained on load is less than 30 ns and the pulse width modulation range is about 30%.