Abstract: Epoxy resins for pultrusion are widely used in industry due to their excellent mechanical properties, short molding cycles and low cure shrinkage. However, they have poor toughness after curing and are easily damaged and cracked under external impact. The silane coupling agent (KH550) was used to surface modify the nano-SiO₂, and modified nano-SiO₂ (KH550-SiO₂) was blended with pultruded epoxy resin to investigate the effect of different contents of KH550-SiO₂ on the properties of epoxy resins for pultrusion. A combination of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and rheological testing was employed to characterize the structural features, thermal stability, and rheological behavior of the modified systems. SEM results revealed that KH550-SiO₂ was uniformly dispersed in the epoxy matrix. Mechanical testing showed that, at a loading of 2% (mass fraction) KH550-SiO₂, the tensile strength, tensile modulus, elongation at break, and fracture toughness were increased by 8.43%, 7.80%, 46.05%, and 25.00%, respectively. Moreover, TGA and rheological analysis indicated that the incorporation of KH550-SiO₂ did not negatively affect the thermal stability or processability of the pultrusion epoxy system. This study demonstrates that silane coupling agent KH550-SiO₂ serves as an effective toughening method to significantly improve the mechanical properties of epoxy resins for pultrusion while maintaining their original heat resistance and rheological properties.