To study the effect of silane coupling agent (KH560) and nano-SiO2 synergistically KH560 modified basalt fiber (BF) on the mechanical properties of concrete, KH560 was used to surface modify for BF to produce KH560-BF, and nano-SiO2 and KH560 were used to modify BF to produce SiO2-KH560-BF. Orthogonal tests were used to screene high-strength modified fibers, and the effects of mass fractions of nano-SiO2 dispersion, lubricant and KH560 on the filament bundle strength of SiO2-KH560-BF were investigated. The mechanical properties of modified concrete at 7 and 28 d were evaluated and the microstructure of the concrete was characterized by SEM and EDS. The results show that the optimal upper agent composition for SiO2-KH560-BF is nano-SiO2 dispersion 1.6%, lubricant 0.4%, and KH560 0.5%, and the degree of influence of the three factors is nano-SiO2 dispersion>KH560>lubricant. Compared with KH560-BF, the fiber tow strength of SiO2-KH560-BF increases by 8.62%, tensile strength increases by 4.41%, Si content increases by 24.9%, and there were fewer agglomerated buildups in the SEM images of SiO2-KH560-BF than those of KH560-BF. The 7 and 28 d compressive, split tensile, and axial compressive strength enhancement effects of the concrete with a moderate amount of SiO2-KH560-BF are higher than those of the concrete with KH560-BF.