To meet the demand of modulator power supplies, such as klystrons with output pulses of up to milliseconds, this article describes a long pulse high-voltage pulse power supply based on the Marx circuit. It uses solid-state semiconductor switches as the main discharge switches. Introducing independent charging semiconductor switches at each stage of the Marx units, it solves the limitation of Marx structures that use resistors to charge energy storage capacitors and cannot operate at high repetition rates. In addition, adding an auxiliary power supply to power the driving circuit of each stage’s Marx unit semiconductor switch, it can output long pulses of up to 1ms or more when triggered by optical fibers. The verification device designed using this Marx circuit has 6 basic charging and discharging units, which can output long pulses with an amplitude of -10 kV/1 A and a width of 1 ms. When outputting short pulses, the maximum output frequency exceeds 50 kHz.