CeO2/hydrothermally treated red phosphorus (HRP) heterojunction composite was formed to address the easy recombination of carriers. The results of the composition proportion optimization revealed that the 5%CeO2/HRP composite (weight proportion of CeO2 about 5wt%) showed the best photocatalytic degradation performance for Rhodamine B (RhB). The rate constant value of 5%CeO2/HRP was 0.071 min−1, which was 2.0 and 35.5 times more than that of pure HRP and CeO2. In addition, the introduction of the heavy metal Cr(VI) to form a mixed heavy metal-organic pollutant solution significantly improved the removal of RhB due to the simultaneous removal of the two target pollutants could improve the utilization efficiency of photogenerated carriers. Mechanistic investigations proved that the heterojunction could be decreased the recombination ratio of photogenerated electron-hole pairs in single semiconductors, thereby enhancing its photocatalytic activity. This research not only offered a novel method for designing heterojunction photocatalytic materials, but also provided a fresh perspective on the treatment of mixed pollutants.