Aiming at the problem of Brillouin scattering threshold and sensing characteristics for the distributed optical fiber sensor based on Brillouin scattering, the calculated expression of the Brillouin threshold was received through the coupled equation between the pumping and Stokes wave in optical fiber. Through calculation and analysis the relationship between pulse width, fiber radius and temperature of the relationship with the incident light, theoretical estimation model of Brillouin threshold for pulsed light was proposed for estimating the model theory of optical pulse threshold based on Brillouin scattering. In the experiment, the power relationship between the incident light and scattered light was received using Brillouin optical time domain reflectometer system. By comparing the threshold power under the various definitions, it’s found that the experimental results are consistent with the theoretical calculations.