In the recent years, rapid growth of the world’s population and overutilization of fresh water resources have caused fresh water shortage crisis in the world. In spite of the agricultural activities in the Northern beaches of Iran and also severe decrease of the ground water level, it still has not taken any effective measures to desalinate Caspian Sea water in large scale. In this research, desalination of Caspian Sea water by Silica Nano-Particles with the diameter less than 50 nano meters for agricultural usage has been studied. In this study, by primary experiments the concentrations of the studied parameters including Electrical Conductivity (EC), Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg) and Turbidity of the sea water raw sample were measured. By useing of Jar Test, various dosages of Silica Nano- Particles and the wide ranges of pH were examined. The results show that the 0.45 gr/lit of Silica Nano-Particles is the optimum dosage and pH=10 is the optimum pH for desalinating of Caspian Sea water. Meanwhile, the results revealed the extraordinary effect of Silica Nano-Particles on the studied parameters and has reduced their concentrations significantly so that the concentrations of Na, K which are the most important factors for water salinity, reached to zero.