Abstarct: With the indiscriminate extraction of groundwater from the alluvial aquifer of Yazd, which is the most important aquifer in central Iran in arid regions, it has led to a sharp drop in the water level and a decrease in the available and extractable water reserves in this region. therefore, determining the origin and studying the hydrogeological, hydrochemical-isotopic behavior, as well as determining the water balance and calculating the sustainable yield from the groundwater resources of Yazd Plain, in line with the optimal management of yield and sustainable development in this critical plain, is essential. The direction of the groundwater flow in the alluvial and Unconfined Aquifer of Yazd is mainly from the south side and Shirkuh heights towards the center and the northwest side of the basin (Charkhab area). the water level loss in the Yazd aquifer ranges from 0.1 to 1 meter annually. but in some piezometers, especially in the suburbs of Yazd, the water level has risen by 2.2 to 14.9 in the 20-year period. the depth of the groundwater level decreases from the south and southeast to the center of the plain and then to the northwest and varies between 90 and 150 meters. According to Bilan's calculations, the decrease in the volume of the Yazd aquifer is about 45 million cubic meters per year. In general, in the direction of the groundwater flow, the electrical conductivity increases and varies between 352 and 18580 μS/cm. Neogene sediments in the eastern and southern parts of the plain have changed this pattern and brought in salty water from the surrounding areas. The dominant type of fresh water is magnesic-calcic chloride to magnesic-calcic bicarbonate, and for salt water it is mainly sedic chloride. The main source of salinity in this region is the dissolution phenomenon of evaporites and mixing in the boundary areas of the aquifer. baxsed on the isotopic data of daily precipitation during one water year in Yazd-Ardakan study area from 11 rain gauge stations, the local precipitation line is drawn and presented as δ2H (‰)= 4.45 x δ18O(‰) - 7.45(R2 = 0.95) . A slope less than 8 indicates that evaporation from falling precipitation has occurred. the studied area was mostly influenced by the air fronts of the Mediterranean region and the Persian Gulf. The groundwater samples of the studied area have atmospheric water origin and the evaporation process did not have a great impact on the isotopic behavior of these samples. the samples are in the isotopic range of snow samples. Considering that the main source of water supply to the Yazd plain is the surrounding snow-collecting heights, the location of the samples can be justified. In this research, the amount of sustainable yield from groundwater resources has been investigated using the groundwater balance with modeling in the baxse period of 30 years (from 1401 to 1430) in two scenarios. In the first stage, recharge and yield from the aquifer for the model numerical, fixed, and in the second stage, constant recharge and variable yield have been determined. If the yield from the aquifer continues without change at the rate of about 123 million cubic meters per year, with the passage of time due to changes in the inflows and outflows amounts, the amount the aquifer storage deficit decreases and the aquifer reaches a balance after more than 23 years, but with a reduction of more than 40% of the aquifer's yield, the positive balance and changes in the reserve reach zero. the expected sustainable groundwater yield rate of the Yazd aquifer is about 73 million cubic meters per year.