Distributed optical fiber sensing system based on Brillouin scattering has attracted a widely attention as it can simultaneously obtain the continuous distributed information of time and space in the measured field. A novel Brillouin optical time-domain analysis (BOTDA)sensing configuration is presented,called single-ended BOTDA system. A narrow line-width laser was used as the only light source,and LiNbO3 electro-optics intensity modulator was adopted to modulate tunable frequency shift pulse pump light generated by incident light,the pump light with detection light reflected by fiber Bragg grating (FBG)was carried out Brillouin scattering amplification. Through detecting optical power of detection light,Brillouin loss of the whole fiber was obtained with the different line-widths by linear weight spectrum of Lorentz and Gaussian function and Levenberg-Marquardt algorithm. Experimental results show the sensing structure is suitable to distributed measurement,and it has certain reference to the development of BOTDA.