Abstract: 2- (2-hydroxyphenyl) -4 (3H) - quinazolinone (HPQ) is a small chemical entity with the simultaneous characteristics of aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT). Featured with emitting fluorescence in solid state and anti-diffusion ability due to weak lipophilicity and hydrophily, it is suitable for in situ long-term fluorescence imaging after response to the corresponding analytes in biological systems. We first elucidated the luminescence mechanism of HPQ in solid state, then summarized its application in the detection of metal ions and the visual imaging of biomarkers in physiological and pathological processes, in order to provide some references for the development of more safe and effective fluorescent imaging agents based on HPQ.