Abstract: To explore the effect of surface modification of basalt fibers (BF) on the sulfate resistance of concrete,γ-aminopropyltriethoxysilane coupling agent (KH550) and nano-silica (nano-SiO₂) were used to modify the surface of basalt fibers (BF). The modification mechanisms were revealed through micro-characterization techniques and concrete sulfate erosion tests, and the durability in a sulfate erosion environment was assessed. The results show: KH550 can facilitate the uniform distribution of nano-SiO₂, which aids in the reaction between nano-SiO₂ adhered to the BF surface and Ca(OH)₂ in cement, enhancing the hydration of cement and the interfacial adhesion between BF and the cement matrix. Under sulfate attack conditions, concrete that incorporates nano-modified fibers outperforms other types of concrete in terms of salt resistance and compressive strength. After 280 days of erosion, there is merely a 0.23% reduction in the mass of the concrete and a 2.76% decline in its compressive strength. The erosion process of concrete specimens under sulfate dry-wet cycling can generally be divided into three phases: enhancing the compaction of concrete, starting concrete deterioration, and severe degradation of concrete. Nano-SiO₂ fills the micro-cracks at the interface between fibers and the matrix in concrete, leading to secondary hydration reactions that produce dense and durable C-S-H gel. This effectively inhibits the further penetration of chemicals and moisture into the concrete, impedes the production of expansive materials such as AFt and gypsum, significantly improving the concrete’s resistance to salt-induced erosion.