In order to describe the quantitative relationship between soil salinity in the profile of a saline alkali?soil and leaching water volume, the effects of leaching water volume on soil water and salt movement in a typical saline alkali?soil in Ningxia Province treated with desulfurized gypsum were studied by an indoor soil column leaching test. The results showed that applying desulfurized gypsum had a positive effect on increasing water infiltration, reducing soil pH and salinity of the 0-20 cm soil layer, and soil desalinization rate was between 84.39% and 95.41%, but large leaching water volume might aggravate soil alkalization. Under?continuous leaching condition, the maximum desalting depth lied in the 60-80 cm soil layer. In the 0-20 cm soil layer, the?desalting?ratio of Cl- and Na+ had a small variation with the increasing amount of leaching water volume. Under small leaching?water volume, the?desalting?ratio of SO42- was lower than those of Cl- and Na+. Under large leaching?water volume, the?desalting?ratios of three ions were very close. In the 20-40 cm soil layer, the?desalting?ratio of major salt ion was in a descending order of Cl- > SO42- > Na+, and it increased quickly, finally remained stable. Under small leaching?water volume, Cl-, Na+, SO42- accumulated in the 40-60 cm soil layer. Under large leaching water volume, they continued downward migration. When leaching?watervolume reached 60 cm, SO42- and Na+ accumulated in the 80-100 cm soil layer, while Cl- migrated to >100 cm soil layer.