The scattering optical signal of BOTDR based on Brillouin scattering distributed sensor is very weak and have a frequency width of several decades megahertz,so it is hard to perform the traditional coherent demodulation.A optical heterodyne detection based on Hilbert transform is presented here.In detail,Brillouin back-scattering light is heterodyne detected with the reference right which is modulated by microwave electric optical modulator to produce frequency-adjustable light,then the detected photoelectric signal is demodulated using Hilbert transform.At last the distributed sensing signal with better S/N ratio is gained,which can enhance the performance of the sensor.