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Currently, the hidden risk of microplastics in the coagulation process has attracted much attention. However, previous studies aimed at improving the removal efficiency of microplastics and ignored the importance of interactions between microplastics and natural organic matter (NOM). This study investigated how polystyrene micro/nano particles impact the release of NOM during the aging of flocs formed by aluminum-based coagulants Al 13 and AlCl 3. The results elucidated that nano-particles with small particle sizes and agglomerative states are more likely to interact with coagulants. After 7 years of floc aging, the DOC content of the nano system decreased by more than 40%, while the micron system did not change significantly. During coagulation, the benzene rings in polystyrene particles form complexes with electrophilic aluminum ions through π-bonding, creating new Al-O bonds. NOM tends to adsorb at micro/nano plastic interfaces due to hydrophobic interactions and conformational entropy. In the aging process, the structure of PS-Al 13 or PS-AlCl 3 flocs and the functional groups on the surface of micro/nano plastics control the absorption and release of organic matter through hydrophobic, van der Waals forces, hydration, and polymer bridging. In the system with the addition of nano plastics, several DBPs such as TCAA, DCAA, TBM, DBCM and nitrosamines were reduced by more than 50%. The reaction order of different morphological structures and surface functional groups of microplastics to Al 13 and AlCl 3 systems is aromatic C-H > C-OH > C-O > NH 2 > aromatic C C > aliphatic C-H and C-O>H-C O> NH 2 >C-OH> aliphatic C-H. The results provided a new sight to explore the effect of micro/nano plastics on the release of NOM during flocs aging. [Display omitted] • Polystyrene plastic particles complex with Al-based coagulants through Al-O bond. • Nano-plastic particles with small sizes are more likely to interact with coagulants. • Micro-nano plastics would affect the reactivity order of functional groups of NOM. • Flocs formed with plastic would adsorb and release NOM in the aging process. • The involvement of Micro-nano plastics may increase the formation of DBPs. [ABSTRACT FROM AUTHOR]