In this study, we prepared carbon quantum dots (CQDs)-modified 26-facet Cu/Cu2O composites and investigated their photocatalytic degradation effect on methyl orange (MO). The microstructure and composition of the reduction products were analyzed. The test results validate the successful modification of CQDs on the surface of Cu/Cu2O composites. Further, through electrochemical performance analysis among the materials with different thiourea dioxide (TD) contents, 3TD (n × 0.00075 mol of thiourea dioxide is defined as nTD) exhibits the strongest electron transfer ability; thus, 3TD was selected to further combine with CQDs to examine the photocatalytic performance of Cu/Cu2O composites. We analyzed the photocatalytic behavior of the composites by monitoring the degradation of the MO solution. Based on the photocatalytic performance test, the CQDs/3TD composite exhibits excellent photocatalytic activity. Following 120 min of visible light irradiation, the degradation rate of MO with the addition of loaded CQDs increased from 25 to 73%. Materials with both adsorption and photocatalytic properties were successfully prepared, which resolved the regeneration of adsorbents to a certain extent and further accelerated the degradation of dyes.Graphical Abstract: