Recycling of fly ash (FA) and red mud (RM) is one of the most environmental challenges. In this study, the catalytic performance of fly ash-red mud particle electrodes (FRPEs), which were prepared with FA and RM under different ratios, were applied in three-dimensional electrochemical system (3DES) for wastewater treatment. Different ratios, cell voltage, initial pH and FRPEs dosage on the degradation of Atrazine (ATZ) were investigated. As a result, 90.1% of degradation rate toward ATZ was achieved as followed the optimal conditions: fly ash: red mud = 3:4, FRPEs dosage 100 g/L, cell voltage 5 V, initial pH 6.8 and treatment for 30 min. Additionally, FRPEs still maintained the high activity after 7 recycles, proving the stability and recyclability of the FRPEs in 3DES. The possible reaction mechanism of 3DES and the degradation pathway for ATZ were also proposed via controlling and free radical quenching experiments. The results indicated that ·OH is the main active free radical to degrade ATZ and the process mainly occurs on the surface of FRPEs. This research provides a new strategy for wastewater resources utilization of fly ash-red mud and broad prospect for the applications of 3DES.