Abstract: Because the isolation performance of Raman filter is not high,a new demodulation method is proposed to suppress the system background noise,heat excursion accumulation and anti-Stokes backward scattering intermingled with Rayleigh backward scattering.The new method can improve the temperature precision,stability and sensitivity of system and reduce the system cost with the constant temperature groove abrogated.The experimental results show its measurement precision is better than 0.05℃.