As a special kind of wideband high-power microwave source, the GNLTL (gyromagnetic nonlinear transmission lines) have drawn much attention due to the characteristics of high center frequency, easily implementation of frequency adjustment, high repetition frequency, etc. In order to clarify the special working mechanism of GNLTL, the differences between GNLTL and the traditional magnetic applications were compared and analyzed. Starting from the microscopic magnetization dynamics, a qualitative explanation was provided for the reasons of microwave generation at GNLTL. A low-power validation experimental setup was built, with a focus on introducing the construction of experimental scenarios and GNLTL design. Microwaves signals are generated in the experiment with a center frequency of 750 MHz, a 3 dB bandwidth of 12% and a peak power of 245 kW, the microwave generation effect of GNLTL is preliminary verified.