This paper presents a simulation study of vacuum membrane distillation (VMD) for desalination. A simulation model was built on the Aspen Plus platform as a user defined unit operation for the VMD module. A simplified mathematical model was verified, and the analysis of process performance based on simulation was also carried out. Temperature and concentration polarization effects are significant in the conditions of higher feed temperature and/or vacuum pressure. The sign of (P-I,P-f - P-I,P-p), difference of the vapor pressures between the membranes at the interfaces, is an indicator of the vacuum pressure threshold. Increasing the vacuum pressure at lower feed temperature is an effective way to increase the permeate flux and reduce the energy consumption simultaneously.