Abstract: Stacked Blumlein pulse forming networks (PFNs) with photoconductive semiconductor switches can be used to drive flash X-ray diodes. In order to increase allowable running voltage of the device, factors affecting overvoltage on ceramic capacitors for PFNs during discharge are investigated. A voltage wave model of the stacked Blumlein PFNs is established, which incorporates parameters such as switch turn-on delay time, conductive resistance, and arbitrary resistor load, and the results are in accordance with that of PSpice circuit program. Moreover, factors influencing overvoltage coefficient are discussed, which shows that switch synchronization is key to overvoltage, the decreasing of diode impedance enhances the overvoltage coefficient, and too early collapse of diode impedance boosts the overvoltage up to－3 times the charge voltage.