In this paper, we have presented a convenient strategy to fabricate Cu-doped carbon quantum dots (Cu-CQDs) for H₂S sensing and imaging applications. Cu-CQDs are obtained by one step hydrothermal carbonization, using ethylenediaminetetraacetic acid salts and cupric chloride as sources, which simultaneously incorporates Cu (H₂S-responding site) and a luminescent carbon quantum dot (fluorophore). Thus, the added NaHS (H₂S donor) can lead to the fluorescence quenching of Cu-CQDs, and such a fluorescence response allows the detection of H₂S in the range of 2–500 μM with a detection limit of 0.5 μM (S/N = 3). In addition, confocal imaging was achieved successfully in living cells.