Potable water Supply has a significant role in today's developing world. It is very important to determine the specifications of desalination systems in order to achieve cheaper water prices and better operational conditions. Multi-effect desalination (MED) with thermal vapor compressor (TVC) is a progressing, low cost and easy operating system to produce drinking and pure water for both social and industrial applications. In this paper, the effects of different design parameters such as number of evaporation effects, inlet steam pressure, temperature difference of the effects, and feed water temperature on MED system specifications, i.e. performance ratio, required heat transfer area and cooling sea water, are studied. The results show that there is an optimum value for the number of effects for a system with constant production capacity. This optimum value is a function of seawater salinity, effects temperature difference and feed water temperature. The results also show that the increase of inlet steam pressure increases the performance ratio and the required heat transfer surface area of the system and decreases the cooling seawater mass flow rate.