A Nafion-based amperometric sensor utilizing Pt-Sn/C sensing electrode was developed to realize the effective detection of H₂S at room temperature. We compared the morphology and gas-sensing properties of two kinds of Pt/C materials prepared by the sodium borohydride reduction method and the ethylene glycol method and found that the latter was significantly better. Pt-Sn/C prepared by the latter method has a uniform morphology and high catalytic activity and achieves efficient detection of H₂S. The sensor could detect 0.2–100 ppm H₂S linearly with a sensitivity of 0.276 μA/ppm. More importantly, the response-recovery time to 50 ppm H₂S was 10 s and 8 s, which signified a very fast rate. Furthermore, the device also exhibited superior selectivity and long-term stability. Such a device has a good application prospect because of its many advantages.