Ａ method of designing a low impedance, lumped parameter, nonuniform capacitance pulse forming network(PFN) to fit in with the needs of a high voltage, large turns ratio ,low impedance pulse transformer with large leakage inductance are introduced.Combining with computer optimization design, a 100kV, 1.4Ω, 6 stage lumped parameter Blumlein network has been achieved, shortened the rise time and fall time of output pulses, improved pulse waveform and successfully used in a 500kV long pulse accelerator.