Objective:To study the effect and underlying mechanism of sulfur-fumigation and water-soaking on total ash of Di-oscoreae Rhizoma, find the key factor( s) affecting the total ash of Dioscoreae Rhizoma, and explore the rationality of ash limits of Di-oscoreae Rhizoma described in Chinese Pharmacopoeia. Methods:Dioscoreae Rhizoma was respectively dealt with sulfur-fumigation and water-soaking. The changes in total ash content of Dioscoreae Rhizoma was detected by the ash determination methods for total ash and SO2 described in the pharmacopoeia, and then the ash content change of inorganic salts was used to study the mechanism. Results:Sulfur-fumigation could slightly reduce the total ash content of Dioscoreae Rhizoma, while significantly reduce the ash content of calcium oxalate and calcium sulfate with the reduction degree of 7. 20% and 9. 90%, respectively. Calcium phosphate and calcium chloride were slightly affected by sulfur-fumigation, and the results indicated that the effect of sulfur-fumigation on ash content was mainly real-ized by increasing the decomposition rate of calcium oxalate and calcium sulfate. Water-soaking could decline the ash content of Di-oscoreae Rhizoma, and the phenomenon was common in the rhizome medicinal materials. The influence of water-soaking on total ash was more significant than that of sulfur fumigation. Conclusion:Sulfur-fumigation can reduce the total ash content of Dioscoreae Rhizo-ma by increasing the decomposition rate of calcium oxalate and calcium sulfate, however, the effect is mild and the process isn't the key influencing factor in the total ash content of Dioscoreae Rhizoma. During the preparation of Dioscoreae Rhizoma medicinal slices, water-soaking can cause the great loss of water-soluble mineral salts, such as Cl-, C2 O4 2-, NO3 - and SO4 2-, which leads to the reduction of total ash content, therefore, water-soaking is the key influencing factor in the total ash content of Dioscoreae Rhizoma.