Mathematical thermodynamic modeling is used in desalination systems to obtain unknown values and predict various properties such as enthalpy or phase equilibrium. These models are useful to understand system behavior. A mathematical modeling of a multi-effect distillation (MED) plant without a thermal vapor compressor (TVC) was performed to simulate and forecast the temperatures, mass flowrates, and the productivity of each cell of steam. The total productivity of the desalination unit and the performance rate in different operating conditions were also found. A python program was used to solve the model equations. The evaluation indicates that the model is reliable and its predictions matched well with the real data obtained from Zuara desalination plant. This subject was selected for research because most studies concentrate on MED with TVC or MED of low cell number and without TVC. The obtained results show that the productivity of the system and the gain output ratio are directly proportional to seawater temperature and inversely proportional to plant load. The model can be utilized to estimate the performance of desalination plants of MED without TVC. The model was validated using industrial data.