Fluid transport through membrane has attracted broad interests in recent decades due to their close association with wide industrial applications. Whereas massive experimental and simulation studies have been reported, the molecular mechanisms of fluid transport in nanopores are still poorly understood. Herein, we report a non-equilibrium molecular dynamics (NEMD) simulation study for elaborating the confinement effect of water transport through carbon nanotube (CNT) membranes. By varying the tube flexibility, inner surface wettability and pore size distribution (PSD), the permeability of water flow characterized with the flux enhancement rate is extensively examined. In addition, the pore size effect and pore size distribution are carefully taken into account when evaluating the apparent water flux through CNT membranes. We show that these treatments allow us to predict the water flux in a satisfactory agreement with reported experimental measurements. This work provides a quantitative simulation model toward the rational design of high efficient membranes. (C) 2018 Elsevier Ltd. All rights reserved.