Under the size limit of 3m×1.5m×0.2m, a novel ultra-wideband flat antenna of volcano smoke with high octave is presented in this paper based on the loaded resistance technology. The antenna is fed by coaxial line, and the perfect transition from the transmission line (50Ω) to the free space (377Ω) is realized through the optimization of low frequency matching circuit. The optimum low-frequency extended radiation performance is obtained with sweeping parameter simulation. The simulation results show that the voltage standing wave ratios (VSWR) of the antenna is less than 2.5 (S11<-7.2dB) in the frequency range from 300kHz to 300MHz, and the ultra-wideband of 1000 octave is realized for the first time. The experimental results show that the antenna achieves approximately uniform field radiation in the forward direction with high quality waveform fidelity, and the back radiation of the antenna is less than 5%.