Effects of the characteristics of membrane such as water permeability-coefficient, solute permeability-coefficient, and membrane resistivity on the performances of the spiral wound module in the PRO system have been studied numerically. Fluxes of water and solute through membrane, and concentrations and flow rates in the channels were obtained. The water flux through membrane increases almost linearly with the water permeability-coefficient, but it is insensitive to the solute permeability-coefficient. Decreasing the membrane resistivity makes the water flux through membrane and the power density increase. Effects of the membrane resistivity on the water flux through membrane and flow rates in the channels are small when the difference between the inlet-pressures of draw- and feed-channel is large and vice versa. The power density increases and then decreases as the channel-inlet pressure difference increases. The maximum power density is 16 W/m2 at 14 atm of the channel-inlet pressure difference in our system.