Abstarct: Dams are one of the major hydraulic structures that are constructed in all regions of the world, especially in arid and semiarid areas for control and management of surface waters. Their structural behavior and operation are in very strong relation with geological conditions of where they are built on. So all possible risks should be reviewed within the dam site and the reservoir and eliminated or reduced as far as possible. The presence of halite karst systems in dam reservoirs can be one of the crucial sources of pollutants for the water resources. Karst is one of the most amazing phenomenon of the geology that is of great importance due to its narrow interaction with underground waters and superficial waters. Karstic regions are those with dissolving caves. If dam is constructed in the regions with reactive rocks it is likely to be endangered by karst phenomenon, dissolution and corrosion of current waters and construction of dams and reservoirs in these formations are associated with high risk. Comprehensive and accurate understanding of the salt dissolution processes facilitates the descxription of salt karst formations dissolution process in dam reservoirs. Dissolution coefficient is depended to several factors including the characteristics of the solvent and solute, the volume and speed of the involved solvent current, the level of exposure, saturation concentration, temperature, pressure, acidity and the effect of soluble material. This research was performed baxsed on three basis: field studies, experimental investigation and numerical modeling. For determination of dissolution coefficient, the physical model of reservoir was built in a from of trapezoidal channel and samples of salt rock in the reservoir were used in the physical model karst formation. This model was implemented in different conditions and the results of dissolution amount and salt concentration were measured for different time scales. At the next stage, the physical model was simulated in numerical model for determining of dissolution coefficient. The numerical model ran with different dissolution coefficient and results were compared with experimental results. With this comparison and adaptation of results, the dissolution rate of halite karst determined and then used in the numerical simulation of main reservoir. With simulation of main reservoir using dissolution coefficient obtained from laboratory study, the effect of salt karst formation on reservoir water quality was analyzed. The influences of effective parameters such as dissolution rate, air temperature, discharge and relative humidity on the water quality of dam reservoir were studied along with carrying out a wide range of sensitivity numerical analysis. To this purpose, a versatile finite volume tool ‘MIKE’ was used. MIKE is an integrated numerical modelling system that is developed for use in wide range applications like oceans, coasts and harbors, gulf, lakes and dam reservoirs. This model has the ability of two-dimensional and three-dimensional distribution of parameters like temperature, salinity and other reservoir pollutants and analyzing of water quality in downstream. Using the experimental study and numerical simulation and implementation of results, the dissolution coefficient of salt karst formation was calculated about 0.2 cm/h. The results of numerical simulation of reservoir showed that the water quality of reservoir is not in good condition and even in full tank, the salt concentration of reservoir reached to 4000 mg/l which is almost 3 times higher than the allowed limit of 1500 mg/l. Numerical model results showed that early months of operation were not critical to the project and salt concentration in reservoir was in the rang of 0.8 to 0.9 of allowable limit. But considering the changes occuring in reservoir conditions, the process of salinity distribution increases and salt concentration increases with time. By comparing the salt concentration in reservoir and in numerical model, it was found that the average error percentage of concentration values was about 13.65 percent and the numerical model showed the values lower than the reservoir in most times. The sensitivity analysis of parameters affecting the salinity distribution, showed that these parameters have a significant impact on salinity distribution and salt concentration in reservoir. It was found that with 10 percent changes in studied parameters, dissolution rate with 21%, air temperature with18%, discharge with 21.1% and relative humidity with 6.1% caused changes in salt concentration of reservoir. According to the results it is evident that dissolution rate and discharge were the most important factors that influence the behavior of salinity distribution in dam reservoir.