Sulfur dioxide (SO2) is a gas signal molecule, and SO2 and formaldehyde (HCHO) jointly maintain the internal homeostasis of organisms in the complex signal transduction process. Many fluorescent probes have been designed to detect SO2. However, the response of most probes to SO2 was irreversible, and they are not suitable for studying the dynamic interaction between SO2 and HCHO. In this text, we designed a reversible near-infrared fluorescent probe NIR-BN-Acrylate. Benzopyrylium was used as a fluorophore because of its specific site for SO2 reaction (the double bond of the benzopyrylium unit). The detector exhibited near-infrared emission at 665 nm. In addition, NIR-BN-Acrylate had been successfully applied to target mitochondria to detect SO2 in HepG-2 cells and zebrafish. We also monitored the dynamic changes of SO2 and HCHO over time by the fluorescence intensity of NIR-BN-Acrylate. Unexpectedly, through a series of spectrometric titration experiments and NMR titration experiments, we found that the double bond site on the benzopyrylium group was highly reactive and particularly sensitive to SO2, while the other reactive sites had relatively low reactivity and hardly reacted with any substance.