Using carbon nitride photocatalysts to catalyze the selective conversion of biomass platform molecules could not only expand the application fields of non-metallic catalysts but also alleviate the dependence on fossil energy in chemical manufacturing. 2,5-diformylfuran is an indispensable intermediate for the production of value-added chemicals. In this study, pyromellitic dianhydride and melem were used as the precursors. The pyromellitic dianhydride monomer was incorporated into the carbon nitride skeleton by high-temperature heat-treatment, and the catalysts were further treated with H₂O₂. Finally non-metallic carbon nitride photocatalysts containing nitrogen hydroxyl groups were prepared. Moreover, its performance in the selective oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran under visible light excitation was investigated. The results showed that H₂O₂-treated samples could generate nitroxide radicals under light irradiation, resulting in the selective oxidation of hydroxyl groups on the side chains of 5-hydroxymethylfurfural molecules into aldehyde groups, avoiding undesired side-reactions (ring-opening, mineralization reactions, etc.) caused by various reactive oxygen species that may be generated in aqueous solutions. In particular, under the excitation of an LED light source with a specific wavelength (400 nm), when the ratio of melem to PMDA precursor was 1 : 2, the selectivity of 2,5-diformylfuran over the photocatalyst could reach 96.2%.