This paper presents a theoretical analysis on parallel feed LT-MED desalination system with thermal vapor compressor which is helpful to the design and operation of such kind of seawater desalination plant. The mathematical model of a parallel feed LT-MED desalination system with thermal vapor compressor (TVC) is developed on the basis of the mass and energy conservation equations. In the model, the temperature loss is considered caused by the boiling point elevation (BPE) of seawater and the steam flow resistance is also included caused by flowing through tube bundle demisters and pipelines between adjacent evaporators. The property parameters of seawater are taken as the functions of temperature and concentration. A computer program is drawn up to solve the mathematical model. The calculation is based on the system with rated water production 3000 t/d. Taking actual operation into account, the influence of heating steam temperature of the first effect and entrained steam position of TVC on system performance are analyzed. The results show that when other relative parameters are fixed, the gained output ratio (GOR) and the total area of evaporators change slightly with the increasing of the heating steam temperature of first effect under the calculation condition of this paper. The results also demonstrate that there exist suitable entrained steam positions of TVC for the cost of water.