Based on the data observed in fixed location,the variation of soil moisture and its influences on potato yield in the mountainous area of South Ningxia Hui Autonomous Region was investigated.Experimental results indicate that the annual variation of soil moisture content presents a positive parabola shape,which is high in spring and autumn and reaches a bottom in early summer.Dynamic change of soil moisture is mainly dependent on the balance process between the seasonal distribution of annual rainfall and evaporation.Dynamics of soil moisture varies from 9.95% to 21.6% in the whole growth period.The soil moisture content in 0—100 cm soil layer is most remarkably correlated with potato yield.The most remarkable correlation with potato yield is observed in branching period and fruit period which are the peaks of potato water consumption.In this stage,10 mm increase of soil moisture in the layer may increase potato yield by 135~270 kg/hm².