We investigated the influence of carbon nanotube (CNT) size using CNTs including CNT(6,6), CNT(7,7), CNT(8,8), CNT(9,9), CNT(10,10), and CNT(11,11), and the influence of draw solution concentrations, such as 2.5, 3.75, and 5.0 mol·L-1, on the permeation behaviors of salt and water molecules through the biomimetically manufactured forward osmosis (FO) membranes. Nanosecondscale molecular dynamic simulations were carried out to obtain the relevant information, including the distributions of the water molecules, water flux, and salt permeation within the different CNT membranes. Simulation results show that the FO membrane incorporating CNT(8,8) can achieve the highest water flux and also the lowest salt permeation.