When the Tunable Diode Laser Absorption Spectroscopy (TDLAS) analyzer is used to measure the hydrogen sulfide in nature gas, there are strong interferences from light hydrocarbon and CO2 in the natural gas background. Their spectra structure is imposed on the analyze spectra. The spectral interferences affect the extraction of the H2S absorption spectrum. The Partial Least Squares(PLS) algorithm is proposed to deal with the spectral interferences. The Common Least Square (CLS) and the PLS models are adopted in analyzer to evaluate the differential spectrum and direct measurement spectrum of 0~50 ppm H2S in natural gas. PLS is superior than CLS in the analysis of both differential spectrum and direct spectrum. Based the analyzer reading, the absolute error of PLS result with direct measurement spectrum is within ±1 ppm. With PLS algorithm, the analyzer need not to store the mass data of reference spectra, and the complicated differential system can be elimentated from analyzer, which can save the cost and improve robustness and the time response.