Evaluation and modeling of river water quality is of great importance in managing the use of surface water resources. In this study, the water quality of Behesht Abad river, one of the important tributaries of Karun river in Chaharmahal and Bakhtiari province, was studied and evaluated. Beheshtabad River, which consists of two rivers, Junqan and Kiar, has been considered by planners for several years due to the existence of pristine natural resources, boiling springs and its permanence, Therefore, due to the discharge of urban, industrial, agricultural wastewater and as a result of the decline in water quality of this river, water science researchers have to take a closer and deeper look at this region and this river. Therefore, in this study, the water quality of the river has been studied and scientifically evaluated. For this purpose, initially the values ??of water temperature variables, electrical conductivity, soluble solids, dissolved oxygen, biochemical and chemical oxygen demand, ammonium, nitrate, orthophosphate, fecal coliform and acidity in two periods of September 1397 and July 1398 for three stations in June, Kiar and Beheshtabad were harvested, collected and reported. To determine some variables, water samples were transferred to the laboratory in accordance with existing standards and analyzed. According to the values ??obtained in the two periods, water quality was simulated with the QUAL2Kw model. Since water is taken from this river for agricultural purposes and according to the pollutant amounts and the impact of each of them on the water quality of the river, two scenarios were defined to improve water quality (elimination of water withdrawal and withdrawal 3 times the existing amount). Comparison of water quality in each of the scenarios for each period was performed using NSFWQI quality indicators (US Department of Health surface water quality index) and IRWQI (Iran Water Resources Quality Index) that NSFWQI index was more sensitive than IRWQI. In NSFWQI index for September 1397 and July 1398, average quality, also in IRWQI index for September 1397, relatively good quality and for July 1398, average quality were reported. At the end, the water of this river was classified according to the values ??of anions, cations and water hardness, for drinking, using Schuler diagram, and for agricultural use, using USSL diagram. River water was classified as acceptabLe for drinking in October 1397 and July 1398. And for agricultural use, it was classified well in both periods. Keywords: Simulation, Model, Water Quality, Behesht Abad, Junqan, Pollution, QUAL2Kw