Abstract: In order to obtain nanomaterials with better dispersal, filling and barrier properties, which were used as fillers to enhance the protection of the epoxy coatings for cement mortar, the polydopamine (PDA), which was prepared by self-polymerization of dopamine hydrochloride (DA) and silane coupling agent (KH550), was utilized to modify nano hexagonal boron nitride (hBN) and nano silicon dioxide (SiO₂), respectively, to obtain two nanomaterials polydopamine hexagonal boron nitride (PDABN) and functionalised SiO₂ (fSiO₂) by polymerization reactions. A new nanomaterial, polydopamine hexagonal boron nitride-functionalised silicon dioxide (PDABN-fSiO₂), was synthesized, and it was mixed with epoxy to prepare a modified coating. The coating was covered on the surface of cement mortar to enhance its carbonation resistance. The microscopic characteristics of nano materials were observed by FTIR, SEM-EDS and XPS. The modified effect of epoxy coating by nano PDABN-fSiO₂ was analyzed by carbonation experiments and permeability tests. Results indicate that the prepared nano PDABN-fSiO₂ has a layer-particle structure and better dispersion in coating, which can effectively slow down the penetration of CO₂ in the coating. Compared with the blank coating, the carbonation depth of the cement mortar coated with nano PDABN-fSiO₂/epoxy coating is decreased by 68.7%, 72.9% and 64.8% at 7, 14 and 28 days of carbonation, respectively, and the permeability of its coating is decreased by 34.7% at 48 hours. Thus, the epoxy coating with nano PDABN-fSiO₂ can significantly improve the carbonation resistance of cement mortar and reduce its permeability.