Abstarct: One of the obstacles to develop sustainable agriculture is the poor quality of irrigation water. It is important to evaluate the quality and process of underground water quality changes in the sustainable management of water resources in each region. The assessment of water quality is usually baxsed on chemical decomposition and measurement of chemical parameters of water. Measuring these parameters in big area is costly and time-consuming, as result it required to estimating methods for prediction of those parameters. On the other hand, because of the geostatistical nature of these parameters, the use of geostatistical estimates is necessary. In this research, groundwater quality of the Miamay plain of Semnan province was studied for irrigation purposes from 2003 to 2015 using statistical techniques. For this purpose, the average of 14 chemical parameters of water quality including sodium, sodium percent, chloride, electrical conductivity, sulfate, calcium, magnesium, bicarbonate, anions, cations, pH, total dissolved solids, total hardness and Sodium adsorption ratio was used in 27 wells with proper distribution in plain in the period of 2003-2015. The value of these parameters was compared by different irrigation standards and results showed that the waters of the eastern plain in the twelve years studied were classified in terms of Wilcox classification and standard of drop and sprinkler irrigation. The amounts of four parameters include chloride, Magnesium, total dissolved solids and electrical conductivity have exceeded the FAO limits. The waters of the central and western parts of the plain were without FAO problems, in terms of Wilcox, moderate and in terms of drop and sprinkler irrigation, had a low to moderate restriction. The inadequate and medium water quality of the eastern parts, middle and western parts of the plain was confirmed by irrigation indices, zoning maps and trend diagrams in three different parts of the plain. The amount of most chemical water parameters during this time period is increasing, indicating an ever-increasing decline in groundwater quality in the plain. All parameters of the water were correlated at a level of 99%, and the best variogram model was fitted to them, is a spherical and linear model with a strong spatial structure indicating the necessity of using geostatistical techniques in their analysis.