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A Brillouin optical time domain reflector(BOTDR)is commonly used for strain measurement in geological health monitoring.In a conventional BOTDR,an electro-optic modulator(EOM)is generally utilized to produce the pulse probe light.However,the frequent fluctuation of the EOM optimal working point will deteriorate the extinction ratio(ER)and eventually result in the instability of BOTDR measurement results.Hence,a scheme for stably generating the pulse probe light is proposed based on a semiconductor optical amplifier(SOA).Firstly,a SOA is used to produce the probe pulse light launched into the sensing fiber,and coherent detection is designed to obtain the beat signal of the Brillouin scattering and the reference light.Then the microwave frequency-sweeping method and the Levenberg-Marquardt(LM)algorithm are applied to determine the Brillouin frequency shift distribution along the sensing fiber.Specially,a customed compact software core of LM fitting is developed with basic C code to speed the data process.The experiment results show that the BFS measurement accuracy of ±3.74MHz is achieved over a 10.7-kilometer sensing fiber with the spatial resolution of 1.2m,meanwhile the average data processing time is reduced to about 233ms,about 45 times compared to that when using the LabVIEW,which indicates the stable and fast BFS measurement is realized.