This study introduces a novel photoelectrochemical (PEC) sensor for the highly selective detection of sulfur dioxide (SO <sub>2</sub>) using an organic photoactive molecule probe (OPM). OPM is synthesized through a one‐step coupling reaction, featuring a typical photosensitizer D‐π‐A structure. By covalently bonding OPM with a TiO <sub>2</sub> substrate, a PEC sensor is constructed, exhibiting a significant photocurrent response under visible light excitation. The specific addition reaction between SO <sub>2</sub> and OPM disrupts its conjugated structure, reducing the photocurrent response and achieving highly selective detection of SO <sub>2</sub>. The sensor demonstrates excellent performance in real water samples, emphasizing its practical applications.