TiO₂∶Sm³⁺ nanofibers were prepared by electrospinning technology, and Bi/TiO₂∶Sm³⁺ composite fibers were synthesized by in-situ hydrothermal method under the action of sodium gluconate. The phase and composition of samples were characterized by XRD and XPS. The microstructure of samples was observed by SEM and TEM. The photoelectric properties of samples were analyzed by UV-Vis diffuse reflectance spectroscopy and transient photocurrent. The results show that Sm³⁺ enters the TiO₂ lattice and occupies the position of Ti⁴⁺, resulting in the expansion and distortion of TiO₂ lattice. The lattice defects introduced by rare earth doping can increase the Fermi level of TiO₂, increase the surface energy barrier, and reduce the recombination probability of photogenerated electrons and holes on the surface. Metal Bi, through the surface plasmon resonance effect, combined with the rich energy level structure and 4f electron transition characteristics of rare earth elements, the double modification of TiO₂ is carried out to further improve the photocatalytic activity and stability of TiO₂. Under visible light irradiation for 5 h, the degradation effect of Bi/TiO₂∶Sm³⁺ composite fiber for lomefloxacin is the best, reaching 97.37%, which is 1.7 times and 1.3 times that of Sm³⁺∶TiO₂ and Bi/TiO₂, respectively.