Surface modification of photocatalyst is an effective way to improve the photocatalytic performance and can accelerate the separation of photoactivated carriers. In this paper, Carbon quantum dots (CQDs)/BiOCl composites were prepared by a facile hydrothermal method, which further improves the catalytic performance of BiOCl. X-ray photoelectron spectroscopy (XPS) and cryogenic electron spin resonance (ESR) confirm the successful construction of CQDs/BiOCl. Surface photovoltage spectroscopy (SPS), scanning electron microscopy (SEM) and electrochemical characterization show that the presence of CQDs significantly affects the surface state of BiOCl, accelerates the separation of photoinduced carriers, and results in the enhancement of ·O2− in the reaction system. Higher level of ·O2− in the reaction system shows stronger photocatalytic activity. The photocatalytic activity of CQDs/BiOCl was studied by destruction of phenol, rhodamine B (RhB) and tetracycline (TC). The photo-destruction activity of BiOCl toward phenol, RhB and TC is significantly improved by surface modification of BiOCl by CQDs. Interestingly, when the content of CQDs is 15 mL, the degradation capacity of CQDs/BiOCl toward phenol, RhB and TC is 24 times, 4.26 times and 2.4 times of that of BiOCl, respectively. Combined with the observation results, the photocatalytic enhancement mechanism of CQDs/BiOCl was elaborated.