Designing simple, efficient, and environmentally friendly methods to construct high-efficient photocatalysts is an important strategy to promote the further development of the field of photocatalysis. Herein, flower-like carbon quantum dots (CQDs)/BiOBr composite photocatalysts have been prepared via in-situ synthesis by mechanical ball milling in the existence of ionic liquid. The CQDs/BiOBr composites exhibit higher photo-degradation performance for tetracycline (TC) than BiOBr monomer and the commercial Bi₂O₃ under visible light irradiation. For comparison, the different Br sources and synthetic methods are chosen to prepare BiOBr and CQDs/BiOBr composites. Photocatalysts prepared by ball milling and ionic liquid present significantly enhanced photocatalytic performance for removing TC. In addition, the introduction of CQDs could distinctly enhance the photocatalytic performances of pure BiOBr. The reason is that CQDs as electron acceptor effectively separate electrons and holes and inhibit their recombination. The intermediates during photocatalytic degradation were tested using liquid chromatography-mass spectrometry (LC-MS) and possible degradation pathways were given. During degradation, •OH, O₂^•- and h⁺ were identified to be the main active species based on electron spin resonance (ESR) spectra and free radical trapping experiments. A possible mechanism of CQDs/BiOBr with enhanced photocatalytic performances was further proposed.