Optoelectronic oscillator is a new type of microwave frequency source with optoelectronic combination. It can realize signal output with ultra-low phase noise by using optical long-term energy storage. In this paper, the influence of scattering noise in optical fiber on the phase noise of optoelectronic oscillator is studied. The structure of suppressing Brillouin scattering noise based on equivalent broadening of laser line-width by phase modulation is emphatically introduced. Through theoretical formula derivation and experimental verification, it is shown that the above structure can greatly improve the phase noise of optoelectronic oscillator. In the experiment, a phase modulation signal with a modulation frequency of 50MHz and a modulation amplitude of 3.1 is used to broaden laser line-width, and a ultra-low phase noise signal of -157.3dBc/Hz@10kHz at a frequency of 10GHz is obtained.