Abstract: CMSD is a new inhibitor for chalcopyrite and molybdenite separation flotation，which is made from sodium sulfide and sodium hydrosulfide as the main raw material.The infrared spectroscopy detection method and the first-principle calculation method based on density functional theory (DFT) were used for studying the action mechanism of CMSD on chalcopyrite and molybdenite.The results showed that chemical adsorption occurred on chalcopyrite (112) and (101) surface of CMSD，and didn't occur on molybdenite (001) surface.The adsorption of CMSD on chalcopyrite (112) and (101) surface is accomplished through HS- concurrently interacting with Fe atom and Cu atom in two crystal surface.The inhibition of CMSD on chalcopyrite is accomplished through HS- adsorbs on chalcopyrite surface，to reduce the surface free energy of chalcopyrite，affect the adsorption of mixing hydrocarbon oil on chalcopyrite，thus reducing the floatability of chalcopyrite.

Key words: Chalcopyrite, Molybdenite, Inhibitor, Floatability, Chemical adsorption, Surface energy