Abstract: Abstract: Water shortage and soil secondary salinization seriously affect agricultural production in the arid areas of North China. Under the conditions of sharp reduction in the amount of water used from the Yellow River and large scale implement of water saving program, it is important to maintain a farmland ecological environment and soil health. The objective of this research was to use SWAP model to simulate optimal water use for corn during its entire growing season. The Longshen experimental area in Hetao Irrigation District was selected as the area for the research. The experimental area was further divided into south district and north district according to the spatial variation of soil salinity data collected in combination with calculation using geostatistical method of kriging interpolation. A soil water-salinity numerical model SWAP was established in both the districts. After calibration and validation, the model was used to simulate the soil water and salinity content across various hydrological years under different quantity of irrigation water in various maize growing stages, and to predict the minimum amount of water needed for irrigation to achieve the minimum salt accumulation in soil under different hydrological years. Meanwhile, the safety thresholds of soil water and salinity content for farmland at different growth stages were established to save water and control salt content by analyzing the related literatures. The safety thresholds were the maximum values of the soil moisture and salt that crops could tolerate. The range values of the safety water using amount were put forward for the field water and soil environment under different hydrological years from a exquisite and microcosmic perspective. The results predicted by the SWAP model showed that the water consumption in low flow year (precipitation ≤90 mm) was 263-311 mm, and the water consumption in normal flow year (precipitation ≤140 mm) was 198-227 mm, but the water consumption in high flow year (precipitation ≤200 mm) was 106-138 mm. The water saving index in the low flow, normal and the high flow year comparing with the baseline year (precipitation ≤90 mm) were: 0.01-0.17, 0.04-0.16 and 0.06-0.27, respectively. The results above provided information for sustainable use of water for irrigation in the farmland of local and nearby areas. It will be of great significance not only for the agricultural production and utilization, but also for the development of water resources in Hetao irrigation district.