An ultra-wideband random OEO using both stimulated Brillouin effect and Rayleigh scattering effect is proposed, which can generate random oscillating microwave signals covering all frequency bands. By using stimulated Brillouin scattering effect to amplify weak reverse Rayleigh scattering, the microwave signals with random characteristics which is independent of fixed cavity length can be generated. Experimentally, the work realized the generation of ultra-wideband (DC up to 32 GHz) random microwave signals. Compared with previous methods，the proposed random OEO mechanism is realized in an easier way, which can avoid using 1450 nm laser and promote its application in electronic interference.