Copper Company of Baiyin Nonferrous Group Co., Ltd. has produced about 1×10⁵ m³/a waste acid, in which the rhenium content is 5～70 mg/L. In this study, sodium thiosulfate was used as a special kind of good effect precipitant for extracting rhenium from waste acid. Through experimental studies of the mechanism of redox reaction, dosage, reaction time, reaction temperature and the influence of rhenium content on the precipitation rate of rhenium, the authors determined the optimum precipitation conditions. The pilot test achieved good technical indexes: the content of rhenium in rhenium-rich slag reached 1.66%, and the recovery rate of rhenium reached 99.8%. On such a basis, the mechanism of redox reaction of the precipitation agent was discussed. The precipitation method of sodium thiosulfate has the advantages of simple process, high rate of rhenium deposition and friendly environment, and it can therefore be used for efficient extraction of rhenium from waste acid.