In this letter, we have described the establishment of a label-free fluorometric assay to detect adenosine triphosphate (ATP), which can enable the monitoring of the ATP hydrolysis process continuously and in situ. This assay is based on a silole derivative with positively charged modifications, compound 1, that can aggregate on the negative charged ATP template through charge-charge interaction. Because the silole group has strong aggregation-induced fluorescence emission (AIE), we have found that the aggregation could induce strong fluorescence emission and its intensity is positively and linearly related to the ATP concentration. Meanwhile, 1 also shows good discrimination for ATP, where its hydrolysis products ADP, AMP, and adenosine could not induce sufficient aggregation to produce a strong fluorescence signal. These characteristics are sufficient to build up a sensitive fluorescence assay to monitor the ATP concentration change in solution in situ, and we have also verified its usability in studying the reaction process of phosphatase.