在光纤气体传感系统中，为提高检测的灵敏度，需要采取措施抑制系统的各类噪声。通过设计低噪声的前置放大器和光源驱动电路可有效地降低系统的噪声；但对于因光路变化和光在传输过程中偏振态发生变化引起的背景噪声的处理一直是光纤气体传感系统测量灵敏度提高的难点。提出一种基于最小二乘拟合的背景噪声滤除算法。利用参考光栅和法布里珀罗标准具实现对输出信号的光谱重建。在此基础上，利用气体特征吸收峰两边的输出拟合整个输出曲线。将系统的输出与拟合曲线相除，实现系统输出的归一化，有效地滤除了系统的背景噪声，避免了当传感系统背景噪声发生变化时，需要重新采集背景气的繁琐工作，为测量带来方便。

In fiber gas sensor systems, in order to improve the detection sensitivity, it is vitally necessary to make intensive efforts to restrain various noises of the system. Designing low-noise preamplifier and light driving circuit can effectively reduce the system noise, but cannot reduce the noise caused by the changes of optical path. This kind of noise is called background noise, which influences the measuring sensitivity of fiber gas sensor system. Therefore, how to filter the background noise affects the improvement of measurement accuracy. This paper puts forward a method based on least logarithm square method which can easily reduce the background noise of optical gas sensor system. By using reference grating and Fabry-Perot etalon, it can reconstruct the output spectra. A modified least square method is used to fit the envelope of gas absorption lines by using the data of absorption peaks on both sides. Dividing the gas absorption lines by the envelope line of absorption lines, the normalization of output is realized and thus the drift of the background noise curve due to the change of experimental environment can be reduced. This method can avoid data collection again when the background noise is drifting, and brings convenience to measurement.