<p>Basalt fibre-reinforced epoxy composites have attracted increasing attention due to their excellent mechanical properties and chemical stability. However, their long-term durability in acidic environments remains a critical challenge, mainly due to interfacial degradation and fibre corrosion. To address this issue, this study proposes a synergistic surface modification strategy based on phytic acid and silane coupling agents, and investigates the influence of different phytic acid mass fractions on the corrosion resistance of basalt fibre composites. By characterising the surface morphology and elemental changes of the fibres, and combining this with tests on weight loss, electrical properties, mechanical properties and thermal stability, the synergistic modification effects and corrosion resistance mechanisms are comprehensively evaluated. The results indicate that the synergistic treatment with phytic acid and KH550 forms a stable complex film and a roughened structure on the fibre surface, effectively enhancing the bond strength between the fibres and the resin. Within the phytic acid mass fraction range investigated in this study, the composite exhibited the best acid resistance when the phytic acid mass fraction was 5%. Following acid corrosion, the retention rates of both breakdown strength and flexural strength exceeded 90%. The self-corrosion current density decreased to 74.72&#xa0;μA&#xa0;cm⁻², and the weight loss was only 0.207%. This synergistic modification strategy works in tandem to inhibit the acid corrosion process through both physical barrier and interfacial reinforcement mechanisms, providing a green and efficient technical approach for enhancing the long-term stability of basalt fibre composites in complex acidic environments.</p>