Iran is located in an arid and semi-arid part of the world. Accordingly, the management of the water resources in the country is a priority. In this regard, determining the quality and pollution of surface water and GROUNDWATER is very important, especially in areas where GROUNDWATER resources are used for drinking. GROUNDWATER quality index (GQI) checks the components of the available water with various quality levels. To assess the quality of drinking GROUNDWATER of Yazd-Ardakan plain according to GQI in geographical information system (GIS) environment, the electrical conductivity, sodium, calcium, magnesium, chlorine, pH, sodium adsorption ratio, bicarbonate, sulfate, potassium, water hardness, and all substances dissolved in the waters of 80 wells were determined. The samples were obtained from Yazd Regional Water Organization from 2005 to 2014. Using this data, the map components were plotted by Kriging geostatistical method. Then, the map of GQI was prepared after normalizing each map component, switching to a rating map, and extracting the weight of each component from the rating map. Based on the GQI index map, the index point which was 87 in 2005 has increased to 81 in 2014. These maps show a decline in GROUNDWATER quality from west to the east region. This decline in GROUNDWATER quality is due to the existence of Neogene Organizations in the east and geomorphologic unit of the bare epandage pediment in the west. The map removal and single-parameter sensitivity analysis showed that GQI index in Yazd-Ardakan plain is more sensitive to the components of electrical conductivity (EC), total dissolved solids (TDS), and total hardness (TH). Therefore, these components should be monitored more carefully and repeatedly.