Abstract: The photo-self-Fenton collaborative system, which combines Fenton reaction with photocatalytic system, exhibits excellent oxidation ability over pollutants without external addition of hydrogen peroxide. Herein, the PDI-C/Fe³⁺ photo-self-Fenton system, combining carboxylic acid side chain modified perylene diimide supramolecule (PDI-C) and Fe³⁺, is used to obtain an extremely efficient and durable degradation efficiency of Phenol (a model pollutant in phenolic wastewater). The research systematically investigates the catalytic reaction mechanism by examining the changes in the form and content of iron species, the production mechanism and content changes of hydrogen peroxide and the content changes of various active species. The interaction between Fe³⁺ and the carboxylic acid side chain of PDI-C promotes photo-generated electron capture by Fe³⁺ and the resultant conversion to Fe²⁺, accordingly facilitating the separation of photogenerated carriers. On the other hand, the hydrogen peroxide generated in-situ during the photocatalytic process pairs with the effective circulation of iron ions to form a photo-self-Fenton system, which synergically promotes the efficient and durable phenol degradation. It is also found that as the reaction prolonged, α-FeOOH formed on the surface of PDI-C not only results in iron loss, but also leads to the obscuration of light-absorbing sites, thus becoming a non-negligible factor for the decrease of catalytic activity. Notably, acid addition can not only inhibit the generation of α-FeOOH, but also aid the leaching of formed α-FeOOH, enabling an efficient iron ion circulation and the photo-self-Fenton system's efficient operation. The work also identifies two pathways of hydrogen peroxide production and reveals a competitive relationship between ·OH and ·O₂^– in the presence of Fe³⁺. These findings highlight the high efficiency and durability of the PDI-C/Fe³⁺ photo-self-Fenton system in degrading phenol pollutants under visible light irradiation, while showcasing its potential for practical applications due to its cost-effectiveness and simplicity.