Thermal method of saline water desalination is one of the most common process for the production of high-volume fresh water. In this thesis, the multi-stage Flash evaporation (MSF) method is used to produce fresh water. First, the MSF process is simulated by ASPEN PLUS software and the ENRTL equation. For this simulation, the data of MSF saline water desalination unit in Az-Zour, Kuwait, was used. The e-CPA equation of state is programmed by MATLAB software and the results are compared with the simulation file. It is observed that the e-CPU equation of state has provided more accurate results. The error percentage for this equation of state is below 2%, while this value is below 5% for the ENRTL equation. At higher temperatures and pressures, the e-CPA equation of state has better performance. Due to the fact that thermal methods require a lot of energy, it is recommended that these methods be used next to a gas power plant or where energy is cheap. One section of the thesis, the MSF unit is combined with a gas power plant and the water price produced is calculated. Keywords Process simulation, water desalination, thermodynamic modeling, e-CPA