The detecting mechanism and scattering optical signal′s characters of Brillouin scattering distributed sensor are analyzed first, then a novel detecting scheme is presented and demonstrated experimently, which adopts optical heterodyne detection to measure Brillouin scattering signal. In detail, a DFB LD with <1 MHz line width is used as light source, the source is divided into two part, one part is used as pump light which is modulated into optical pulse(100 ns); the other part acts as reference light which is modulated by microwave electric optical modulator to produce frequency adjustable light. Then Brillouin back scattering light is heterodyne detected with the reference right, the detecting photoelectric signal is first converted into digital signal by hi speed A/D, then the digital signal is stored and added, and at last the distributed sensing signal with better S/N ratio is gained. The distributed detecting of temperature and strain are gotten, and a 25 km distributed sensor is achieved with 3℃