Based on the theory of selective absorption of gas in the near-infrared region and the Beer-Lambert law, Raman scattering characteristics of hydrogen sulfide gas are researched. Meanwhile, a broad-band light source is used to detect the concentration of H2S gas. Self-focusing lenses are used as collimating or focusing lens for transmission gas cell. A method using cascaded GRIN lens to increase the optical-path length is presented, and the detection sensitivity of the gas cell is greatly increased by this method. By analyzing the experimental curves of hydrogen sulfide absorption, it is shown that the system sensitivity is 3.672×10-4 μW/(μL/L), and the resolution is 122.5 μL/L.