Abstract: A study of poison in extracting uranium in carbonate leach liquor with quaternary ammonium salt by infrared spectroscopy is here reported, The results show that the substance seriously poisoning the extractant is poly-thionates, S4O2 6-, S3O2 6- and S2O2 6-. The oxidation of sulfide mineral in pressurized carbonate leach and the mechanism of poisoning of quaternary ammonium salt are discussed