A distributed Raman optic fiber sensing system based on field programmable gate array （FPGA） is proposed， which realizes signal acquisition， transmission， and processing. A cumulative iterative average filtering algorithm based on FPGA and a nonlinear wavelet transform threshold denoizing method are proposed to improve the signal-to-noise ratio （SNR） of the system. First， the amplified Stokes and anti-Stokes signals are accumulated iteratively and then averaged. After averaging of 8000 cumulative iterations， the SNR of the system is improved by 36.748 dB. Then the temperature is demodulated， and the temperature information is denoized by nonlinear wavelet transform threshold. Finally， the accuracy of the proposed system’s temperature measurement is ±1.5 °C from the heating experiment.