Sulfur dioxide (SO₂) is commonly used in food processing and preservation processes due to its antioxidant and antibiotic properties. However, it has been documented that excessive intake of SO₂ could cause serious health problems. Therefore, it is very necessary to develop a novel SO₂ probe with excellent performance. Herein, a novel fluorescent probe (Ph-CN) based on the ICT–ESIPT mechanism for monitoring SO₂ with the CN double bond was developed. Furthermore, Ph-CN exhibits various splendid features, such as near-infrared (NIR) and ratiometric detection, real-time detection (<5 s), good selectivity and photostability, large Stokes shift (230 nm) and large emission shift (200 nm). Most importantly, the probe Ph-CN can realize the detection of SO₂ in HeLa cells and in vivo.