"The soil moisture dynamics of potato field in southern Ningxia semi-arid area Is studied."rhe result shoals:(I)The moisture of potato field could be classed into three stages by thevariability，which very obviously cooperated with precipitation and its distribution within sea-(2)The soil moisture dynamics in vertical direction could he divided into three types too;(n)variable greatly layer <0～20cm). <13) slowly variable layer <20一120cm);(C) relativelyateady layer(120一200cm).The authors also analysed the moisture relationship among those three layer,.(3)In the period of duration of early harvested potato，consumed 3l2一394mm of water，it means 350mm，which mainly from irrigation or soil water in former stage and from rlin(all in its later stage. The ground film could save soil water and raising water use efficiency.and alum enhance riped earlier with high yield in the area，combined with cellar一harvesting wateru"e. We could develope local efficient agriculture, It is a reasonal technique way to increasing income for farmers.