In this study, a novel p–n junction photocatalyst of BiOCl/(BiO)2CO3 anchored on RGO was synthesized to enhance the visible light photocatalytic activity. The crystal structure and morphology of the prepared samples were characterized via X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively. The photodegradation performances of the samples were evaluated by photodegrading methyl orange (MO) under visible light irradiation. The results showed that nanoparticles of BiOCl/(BiO)2CO3 were well dispersed on the RGO nanosheets which served as the growth support and the morphology controller. The RGO addition could enhance the photocatalytic performance of the BiOCl/(BiO)2CO3-RGO composites with the maximum degradation efficiency of 99.1% under visible light irradiation compared to the sample without RGO (80%). The improved property was attributed to the fact that RGO effectively separated the electron–hole pairs of the composites. Meanwhile, the possible mechanism of the photocatalysis was proposed, which revealed the transfer of charge carriers and the formation of active substances in the photocatalytic process.