The research of hydrogen sulfide （H₂S） and methane （CH₄） concentration measurement technology is of great significance to petroleum and petrochemical industry.In this paper， a Quantum Cascade Laser （QCL） with a center wavelength of 8.309 μm was selected as the detection light source based on Tunable Diode Laser Absorption Spectroscopy （TDLAS） technology. A 30 m long distance sensing system was established by using Wavelength Modulated Spectroscopy （WMS） technology to measure the mixture of H₂S and CH₄ gases. The experiment mixed H₂S with 5% volume fraction of water vapor for measurement， and it showed excellent absorption characteristics in this band， with less cross-interference. Through sensing experiments， the impact of different sensing distances of 15 m and 30 m on the detection signal was analyzed. By increasing integration time and calculating the signal-to-noise ratio， a minimum sensing limit of 128.75 ×10^-9 m was achieved. Finally， Allan variance calculations revealed that when integration time was 183 s and 142 s， the lowest detection limits for H₂S and CH₄ were 0.593×10^-9 and 1.160×10^-9， respectively. The results provide an effective method for remote measurement of highly sensitive H₂S and CH₄ multi-component gases and ensure safe operation in a variety of industrial environments.