Wideband high power microwave is one of the main development directions of high power microwave in recent years. A wideband high power microwave system with small volume, working in UHF band is developed. The system powered by a 24V battery uses a Marx generator as the driving source. The wideband high power microwave is generated with a quarter wavelength switching oscillator and radiated with a high power microstrip flat plate antenna. The electromagnetic simulation model is established and the key factors are simulated and calculated. The test results show that the center frequency of the wideband high power microwave is 425 MHz, and the peak-to-peak value of the electric field radiation factor is 92kV@1m. The radiation waveform is basically consistent with the simulation results. The application prospect of wideband high power microwave in drone, robot and other platforms is expanded.