Abstract: Switch oscillator is one of the important methods for broadband high power electromagnetic pulse generation. This paper uses the switch excitation coaxial oscillator as an example, the theoretical calculation and simulation as the main means to study the following three relationships: the characteristics impedance of transmission line and switch oscillator energy storage, the characteristic impedance of the transmission line and the antenna impedance, the characteristic impedance of the transmission line and impedance of switch. The results show that the when characteristics impedance of the transmission line is smaller, the oscillator energy storage is higher; the antenna impedance and transmission line impedance ratio increases, the effective output cycle and quality factor increases, and the energy concentration increases, the spectrum bandwidth reduces, the energy efficiency increases first and then decreases; while the transmission line characteristic impedance is very small, the influence of the switch on the output signal is significant. With characteristic impedance of the transmission line decreasing, the center frequency of the output signal reduces, the quality factor decreases, energy concentration is weak and the bandwidth spectrum expands.