It is very necessary to develop real-time, highly sensitive and selective fluorescent probes for hypochlorite (ClO) in living cells owing to hypochlorite's important role in pathological and physiological processes and its short life. Herein, a pyrene Schiff's base derivative was successfully developed for real-time (within seconds), highly sensitive detecting ClO with a low detection limit (5.7 nM) and wide pH range (4.0-11.0) based on nucleophilic addition and subsequent hydrolysis mechanism. The probe has aggregation-induced emission properties and emits yellow fluorescence (544 nm) in PBS solution, while it exhibits blue fluorescence in other organic solvents (426 nm (THF) - 460 nm (MeOH)). The probe can be used to response ClO in A549 cells with low cytotoxicity, a good cell membranes penetration and good biocompatibility. Cell uptake experiment indicates that probe getting into the cells is energy-dependent and is not attributed to endocytosis. Moreover, the probe is successfully used in real water sample to detect ClO and it can be expected to be applied to ClO participated biological and pathological functions in biological systems.