Abstract: The paper presents a high power bipolar pulse forming line based on Blumlein line and peaking-chopping(P-C) switch, and studies its operating principles. A high power bipolar pulse forming line is designed accordingly, and high voltage experiments about the pulse forming line are conducted on the 800 kV ultra-wideband high power pulse source. The effect of P-C switch and length of the pulse forming line on the output bipolar pulse is analyzed. The Blumlein bipolar pulse forming line can output bipolar pulses with peak voltages of -571.9 kV and +550.4 kV, and peak-to-peak interval of 740 ps, for the input pulse with 652.0 kV peak voltage and 2.1 ns width. The peak-peak voltage of the bipolar pulses is 1.72 times that of the input pulse, and the field-range product is 4.54 MV.