Abstract: The effect of different conditions on synthesizing sodium lactate xanthate was studied. The results observed showed that the optimum condition was the molar ratio of lactic acid, CS₂ and NaOH of 1:1:2.1, the reaction temperature of 40 ℃, and the reaction time of 4 h. Under the optimum condition, the yield of the product reached 59.25 %, which was confirmed as sodium lactate xanthate by UV spectrum and IR spectrum. The effect of sodium lactate xanthate on the floatability of natural chalcopyrite and pyrite was studied in detail. With the Materials Studio software, the energy changes of surface interaction of the systems of sodium lactate xanthate and chalcopyrite or pyrite were simulated according to the molecular mechanics and molecular dynamics. The simulation results showed that the inhibitory effect of sodium lactate xanthate for pyrite was stronger than that for chalcopyrite, which were further demonstrated by IR spectroscopic analysis results.