Non-equilibrium thermodynamic theory was used to study the membrane osmotic distillation (MOD) process. A mathematical model was developed to describe the coupled heat and mass transfer during such process, and the expressions for the characteristic parameters in the non-equilibrium thermodynamics model were given. The model was used to investigate the dependences of the characteristic parameters on the system average temperature and concentration and to analyze the relationship between the temperature and concentration differences between the two sides of the membrane for zero or fixed transmembrane fluxes. The entropy generation rate in the MOD process was also investigated. The results show that the total entropy generation rate can be reduced by lowering the membrane effective thermal conductivity or increasing the system average temperature. The concentration and temperature differences to minimize the total entropy generation rate were also identified.