H2S is an important signal molecule in living systems and related with many physiological processes and diseases. Rapid detection of H2S, hence, is important for studying physiological processes and early diagnosis of diseases. Deep insight into the sensing mechanism is significant and inspiring for the design and modification of high-efficiency H2S probes. The current study has theoretically investigated the recognition and fluorescence mechanism of a newly reported high-efficiency H2S probe. The recognition mechanism is determined to be the reaction between the probe and HS- anion, the rationality of which is further confirmed from the fluorescence property of the recognition product. The non-fluorescence property of the probe attributes to a photoinduced electron transfer process, and the turn-on fluorescence upon exposure to H2S exhibits an intramolecular charge transfer property according to frontier molecular orbital analysis.