Pulsed power drive source is a key part of high power microwave technology. The quality of the output waveform of pulsed power drive source directly affects the output of high power microwave devices. Aiming at the oscillation problem of the flat-top output waveform of pulse power drive source, we designed and developed a compact pulsed power drive source based on PFN-Marx, and optimized the waveform. The parameters of PFN-Marx generators with different structures are analyzed by PSpice simulation, so as to determine the number of sections and levels of the PFN-Marx generator; the oscillation problem of the output waveform is converted into the degree of deviation of each extreme point from the reference value in the flat-top area of the waveform. The objective function is constructed with the root mean square error with the minimum flat-top ripple error as the goal, and the circuit model is established in Simulink. Combined with the MATLAB genetic algorithm, the inductance of the PFN is continuously iteratively optimized. Finally, a set of optimal values is determined, and the inductance structure is redesigned to adjust the inductance value conveniently and to achieve quick waveform optimization. The optimized single-stage PFN outputs a waveform with a leading edge of 24.4 ns and a pulse width of 93.6 ns on a 10 Ω load, and it has good flat-top performance. The assembled 7-stage PFN-Marx generator has an output quasi-square wave under a charging voltage of 53.8 kV and a load impedance of 75 Ω. The pulse peak amplitude is 189.2 kV, pulse width is 93.2 ns, rise time is 8.4 ns, decrease time is 33.6 ns, and the ripple coefficient is 3.5%.