Abstract: The copper-molybdenum separation system of a large-scale porphyry copper mine in Jiangxi has the problems of large amount of sodium sulfide, high COD content in the separation flotation backwater, and it is difficult to reuse and treat. By using KMD series new copper depressant instead of sodium sulfide to carry out small-scale tests, molybdenum concentrate products with molybdenum concentrate grade of 49.63% and operation recovery rate of 89.49% can be obtained. The test index is good, and the effective separation of copper and molybdenum is realized. The cost of regent has been reduced from 105.40 RMB/T of bulk concentrate to 88.04 RMB/T of bulk concentrate. Moreover, the better economic effects were obtained. Through the analysis and detection of the backwater generated by the test, the COD value of the backwater generated by the KMD series of copper inhibitors is only 194.2 mg/L, which is 88.83% lower than the COD value of the backwater generated by sodium sulfide, effectively reducing the cost of subsequent backwater treatment.