The advancement of nanotechnology has significantly facilitated the development of thin-film nanocomposite (TFN) reverse osmosis membranes for water desalination. Nevertheless, there are still several issues, including nanomaterial aggregation and low compatibility, that prevent the membrane's performance from reaching the desired level. In this study, graphitic carbon nitride modified with natural tannic acid (TA) macromolecules was adopted as a novel hydrophilic modifier for TFN membranes. The incorporation of this modifier significantly increased the hydrophilicity of the active layer to improve the water permeation ability and formed covalent bonding between the phenolic hydroxyl groups of TA and unreacted acyl chloride groups during interfacial polymerization to enhance nanofiller compatibility with the PA matrix. Consequently, the water permeance of the TFN membrane reached 2.49 L m h bar, which was 2.2-fold higher compared to that of unmodified PA membranes (1.13 L m h bar), while maintaining a high NaCl rejection rate of 96.1%.