The stimulated Brillouin scattering (SBS) effect in optical fiber is studied. The mechanism of SBS effect occurred in a BOTDR system and the application prospect of SBS are elaborated in this thesis. When the extinction ratio of an electro-optic modulator is finite, the spontaneous Brillouin scattering produced by the incident light pulse is amplified by the leaked light through the SBS interaction, which makes the backscattered waveform different obviously from the traditional BOTDR waveform. The time domain expression of SBS power is derived and then simulated numerically with different extinction ratio. The influence of SBS effect on the performance of BOTDR system are analyzed and simulated. Finally, we use the ratio of the SBS signal power in unknown environment with that in known environment to monitor the SBS power change due to the influence of temperature and strain. On the basis of this, the performances of the SBS signal-based BOTDR sensing system such as signal to noise ratio and measurement accuracy are analyzed, which demonstrates the superiority of SBS as a sensing signal.