In the distributed temperature sensing system of Brillouin optical time domain reflectometer based on the electro-optical modulation, the power of reference light exported from the electro-optic modulator will fluctuate while using microwave sweeper.According to the principle of correlation detection, the fluctuations of reference light power will affect the power of Brillouin scattering light, and it will cause large error in temperature measurement.Therefore, a method that can adjust the microwave power based on the output light power feedback of electro-optic modulator has been proposed to keep the power of reference light of Brillouin optical time domain reflectometer stable.The experimental results show that the method can suppress the fluctuation of the first-order edge wave band peak power exported from the electro-optic modulator effectively, and the temperature measuring accuracy has been increased from 6 ℃ to 2 ℃.