Abstract: The paper presents a high power wide band oscillator with nonmatched transmission line which is charged by low impedance forming line. The designs of low impedance forming line and nonmatched transmission line are completed accordingly and high voltage experiments are conducted on the 1 MV Marx generation. The wide band oscillator can output wide-spectrum pulse with center frequency 260 MHz, repeat rate 20 Hz when the gap of main switch is 14 mm with 1.5 MPa SF₆, the gap of chopping switch is 6 mm with 1.0 MPa SF₆, and the gap of peaking switch is 4 mm with 1.1 MPa SF₆. The technology of nonmatched transmission line charged by low impedance forming line can output high power wide band pulse and increase center frequency.