Abstract: The common method of extracting diosgenin from Dioscorea Zingiberensis is acid hydrolysis, but it yields a large amount of wastewater. A new thermal pretreatment technique was put forward in order to avoid wastewater. The dry material which weight is 3kg was treated about 10min on conditions that steam pressure 1.2MPa, temperature 190℃. The raw material’s microstructure, the FTIR spectra and the Thermal analysis (TG/DSC) curves are changed after the thermal pretreatment process. The mechanism of the thermal pretreatment is analyzed. The results show that this thermal pretreatment technique can cause the starch grains to burst, and break the huge cellulosic molecule structure, at the same time the diosgenin is released. So diosgenin can be extracted directly from the thermal pretreated material without acid hydrolysis.