Bismuth sulfide (Bi2S3) and activated carbon nanofiber doped bismuth sulfide composites (Bi2S3/CNFs) were prepared by the hydrothermal method to remove metronidazole (MTZ) from the aqueous solution. The photocatalyst was specified by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy（FT-IR）, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance and photoluminescence（PL）. The results show that the introduction of active carbon nanofibers (CNFs) into Bi2S3 can reduce the recombination rate of the photogenerated-electron-hole pairs and improve the photocatalytic activity. The photocatalytic degradation of MTZ by Bi2S3/CNFs composite was assessed under visible light irradiation. It was found that the photocatalytic activity of Bi2S3/CNFs composite was excellent when the CNFs content was 47% (based on the mass of Bi2S3, the same below), and the removal rate of MTZ was 92% within 3 h. Bi2S3/CNFs composites also showed strong stability and recoverability after three cycles. In addition, the experimental results of active group capture showed that hydroxyl radical (·OH), photogenerated hole (h+) and superoxide radical (·O2-) were involved in the degradation of MTZ on Bi2S3/CNFs, and·OH and h+ were the main active components of the system.