Abstract: The authors investigated the origin of soil water and vertical infiltration recharge of groundwater in thick unsaturated zone of arid area based on the characteristics of water content, stable isotopes (δD and δ¹⁸O) of soil water and soluble salt ions in soil. The results indicate that the vertical profiles of stable isotopes of soil water depict a cyclic variation as well as water content and chloride of soluble salt ions for the uncultivated regions in desert and cultivated and uncultivated regions in oasis. Each cyclic variation indicates one infiltration event that has involved mixture of newly infiltrated water and existing soil water. The lower value of Cl^- content is consistent with the depleted values of δD in each cycle; δD of soil water varies from -124.10‰ to -94.44‰, which suggests that soil water originates from precipitation or snow in winter in desert and in oasis. The vertical infiltration recharge varies in the ranges of 1.29~5.53mm/a, 0.52~1.85mm/a and 0.03~0.08mm/a respectively for the cultivated and uncultivated regions in oasis and the uncultivated regions in desert.