Organic dyes possess high molar extinction coefficient and good fluorescence emission performance in visible and NIR region, thus they are often used in spectrochemical sensing. Generally, organic dyes usually contain a large π system, and are easy to form assemblies with specific structures through weak intermolecular interactions(such as, hydrogen bonds, halogen bonds, hydrophobic interactions, π-π stacking interactions, van der Waals forces.) in solution. The aggregation process is often accompanied by obvious color or spectral changes. If a specific functional group is introduced into a dye molecule, binding with an analyte induces the aggregation or disaggregation to produce obvious spectral changes, which can be used for the detection of the analyte. Supramolecular aggregates can provide multiple binding sites simultaneously, and have adjustable spatial orientation between assembly units and higher local concentration of sensing binding groups. Therefore, photochemical sensing based on aggregation process shows superior sensing sensitivity and selectivity. In this review, the application of the aggregation of organic dyes in photochemical sensing is reviewed based on our own research work in recent years. Three aspects of induced aggregation, disaggregation and aggregation re-arrangement are discussed respectively, and the future research and development direction of such fluorescent sensing systems are also prospected.