Abstract: In view of the problems of environmental pollution and large consumption of reagents in traditional chalcopyrite depressant, it is of great significance to develop new depressant to achieve effective separation of copper and molybdenum. A new type of depressant GX3 was studied. The effects of PAX, depressant concentration and pH value on the floatability of chalcopyrite and molybdenite and the separation performance of copper and molybdenum were investigated by single mineral and mixed mineral flotation tests. The mechanism of action between depressant and minerals was analyzed by contact angle, Zeta potential, infrared spectroscopy and X-ray photoelectron spectroscopy. The flotation results show that when the concentration of PAX is 10 mg/L, the recovery rate of chalcopyrite is reduced to 20% and the recovery rate of molybdenite is 87% when the concentration of GX3 is 500 mg/L at the condition of pH value 8 ～ 12 and kerosene concentration of 20 mg/L, thus achieving efficient separation of copper and molybdenum. The mechanism study shows that GX3 can oxidize the surface of chalcopyrite to form hydrophilic oxides and hydroxides, which inhibits chalcopyrite, but has little effect on the hydrophobicity and surface properties of molybdenite, thus achieving effective flotation separation of copper and molybdenum.