Hydrogen sulfide (H2S) detection remains a significant concern and the sensitivity, selectivity, and detection limit must be balanced at low temperatures. Herein, we utilized a facile solvothermal method to prepare Cu-doped SnO2/rGO nanocomposites that have emerged as promising candidate materials for H2S sensors. Characterization of the Cu-SnO2/rGO was carried out to determine its surface morphology, chemical composition, and crystal defects. The optimal sensor response for 10 ppm H2S was ~1415.7 at 120 °C, which was over 320 times higher than that seen for pristine SnO2CQDs (Ra/Rg= 4.4) at 280 °C. Moreover, the sensor material exhibited excellent selectivity, a superior linear working range (R2= 0.991, 1–150 ppm), a fast response time (31 s to 2 ppm), and ppb-level H2S detection (Ra/Rg= 1.26 to 50 ppb) at 120 °C. In addition, the sensor maintained a high performance even at extremely high humidity (90%) and showed outstanding long-term stability. These superb H2S sensing properties were attributed to catalytic sensitization by the Cu dopant and a synergistic effect of the Cu-SnO2and rGO, which offered abundant active sites for O2and H2S absorption and accelerated the transfer of electrons/holes.