【Objective】 Overuse of Nitrogen (N) fertilizer results in a low N use efficiency and intensive soil nitrate accumulation in arid farmland critical zone of China, which threatens eco-environmental safety. Elucidating characteristics of soil nitrate accumulation and its influencing factors can provide scientific reference for integrated management of water and fertilizers. 【Method】 The Aksu region, a typical arid region, was selected as the study area. Regolith core samples were collected from three drilling sites including XJ1 (40°36′48.7″N, 80°48′14.2″E), XJ2 (41°16′16.2″N, 80°19′9.1″E), and XJ3 (41°20′37.6″N, 80°17′11.0″E) along a topographic sequence from south to north, with depths of 7.75 m, 10.52 m, and 9.91 m, respectively. The drilling sites were located in a 60-year-old cotton field, a 32-year-old apple orchard, and a 15-year-old apple orchard, respectively. Key soil properties were measured and their relationship to soil nitrate concentration accumulation was analyzed using linear and nonlinear correlations. 【Result】 Significant accumulation of soil nitrate concentration was found under cotton fields with a low altitude and apple orchards with different planting years and a high altitude. Soil nitrate concentrations at depth can reach 44 mg·kg^-1 and soil nitrate accumulation occurs deeper than 10 m. Key soil properties including soil water content and soil particle (gravel, sand, silt and clay fractions) sizes could explain about 50% variations of soil nitrate concentrations with depth. Among key soil properties, soil water content and soil particle sizes were found to be the main factors determining soil nitrate accumulation at depth. Soil nitrate concentration was generally accumulated under conditions with a high soil water content and a fine soil particle. Notable denitrification below the groundwater table at a depth of 4 m occurred under cotton fields and led to a low nitrate concentration below 1 mg·kg^-1. Notable denitrification was not observed below 10 m under apple orchards with a deep groundwater table and soil nitrate concentration was intensively accumulated beyond the root zone deeper than 5 m. 【Conclusion】 Soil water content was found to be the below-ground direct factor determining soil nitrate accumulation at depth. Soil particle sizes were found to be the fundamental factor determining soil nitrate accumulation via controlling soil water content variations.