By rationally introducing aromatic carboxyl functionalized 1,8-naphthalimide, a water soluble fluorescent chemosensor (DA) was successfully synthesized. It could selectively and sensitively detect CN- in pure water via an intramolecular charge transfer to twisted intramolecular charge transfer (ICT-TICT) state change mechanism. The detection limit of the chemosensor DA to CN- was 1.38 × 10−8mol L-1 which was lower than 1.9 µmol L-1 (set by the World Health Organization (WHO)). Notably, DA displayed rapid response (about 1 s) for recognizing CN- in pure water. Furthermore, DA could be applied to monitoring CN- in tap water. Meanwhile, we prepared the test strips based on DA, which could rapidly and efficiently detect CN- in water.