The technique of Brillouin scattering-distributed optical fiber sensing has been presented and demonstrated experimentally. Brillouin scattering light is very weak, has frequency shift with the Rayleigh scattering light. So microwave electric optical modulation is adopted to produce frequency-adjustable reference light, which is heterodyne detected with Briilouin back-scattering light. The detecting photoelectric signal is first converted into digital signal by hi-speed analog-digital converter, then the digital signal is stored and added, at last the distributed sensing signal with better signal-to-noise ratio is gained. The experimental procedures and results are presented. The results show that the frequency and light intensity of Brillouin scattering light vary with the change of temperature. The 25 km distributed sensing of temperature is achieved, and the primary results confirm that the configuration is feasible.