The composition of cutting fluid wastewater is complex, containing oil and various additives. Due to different production processes, various metal particles will be mixed, which has caused great difficulties in wastewater treatment. In this study, electro-flocculation-multiphase Fenton/ultrasound system was used to treat cutting fluid organic wastewater. Firstly, the demulsification pretreatment was carried out by electroflocculation method, which achieved 97.4% COD_cr removal efficiency. Afterwards, a multiphase Fenton/ultrasonic system was used for advanced treatment. By comparing the SEM results, BET results, XRD results and COD_cr removal efficiency of the catalysts prepared by different supports and methods, CuO/CeO₂ catalyst prepared by the deposition precipitation method was used in this experiment. The dissolution rate of copper in the catalyst CuO/CeO₂ was only 1.29% after 4 hours of reaction. After 5 times of recovery, the recovery rate of the catalyst was still 95%, and the removal efficiency of COD_cr was 29.8%. It proved that the catalyst CuO/CeO₂ had good stability. Compared with a separate multiphase Fenton or ultrasound system, the multiphase Fenton/ultrasonic system had a better processing effect. Under the conditions of an ultrasonic frequency of 800 KHz, a reaction time of 180 min, a catalyst dosage of 1.6 g/L, a hydrogen peroxide dosage of 0.5 mol/L, and an initial pH of 8, the multiphase Fenton/ultrasonic system could achieve 65% COD_cr removal efficiency. This study found that electro-flocculation-multiphase Fenton/ultrasonic system could finally achieve 99.09% COD_cr removal efficiency.