Graphitic carbon nitride (g-C3N4) nanostructures were successfully assembled on silica nanofibers (SiO2 NFs) by an electrospinning technique. Then, BiOI nanosheets (NSs) were uniformly grown on SiO2 @g-C3N4 NFs via a facile impregnation method at room temperature. Adjusting the cycle times of the impregnation easily controlled the amount of BiOI NSs on the SiO2@g-C3N4/BiOI NFs. These composite nanofibers exhibited much enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light irradiation. The first-order rate constant of SiO2@g-C3N4/BiOI NFs was nearly three times that of SiO2@g-C3N4 NFs, and seven times that of SiO2@BiOI NFs. The enhanced photocurrent densities, decreased photoluminescence intensity, and shortened transient photoluminescence life time of SiO2@g-C3N4/BiOI NFs all confirmed the improved charge separation. Active species trapping and electron spin resonance-trap technique demonstrated that the photogenerated holes, (OH)-O-center dot and O-center dot(2)- are active radicals in the degradation process. And the loaded heterojunctions display a Z-scheme system in photocatalysis. The SiO2@g-C3N4/BiOI NFs with high photocatalytic activity could be easily separated by sedimentation due to the three-dimensional porous network structures of the SiO2 NFs support. Also, the SiO2@g-C3N4/BiOI NFs exhibited high stability and could be reused without much decrease in photocatalytic activity after several recycles.