Abstract: Parasitic transmission lines located between the stages have severe impact on the output waveform of a PFN-Marx generator. In this paper, the discharging processes of the parasitic transmission line in two kinds of PFN-Marx generators are analyzed. Especially, a two-row structure PFN Marx was simulated by the full circuit simulation. The simulation results show that the dropping of the rising edge of the output waveform was caused by the diode load, the parasitic oscillation frequency was decided by the parasitic capacitance and the amplitude of the parasitic oscillation was amplified by the load inductance. The following experiments proved the results. A de-oscillation circuit was proposed and also proved by the circuit simulation. Further experiments confirmed the validity of this circuit.