A numerical approach is developed to determine the real-time Net Water Transport Coefficient (NWTC) based on the experimental water vapor pressure for the cathode and anode outlet obtained by the optical humidity sensors with Tunable Diode Laser Absorption Spectroscopy (TDLAS). The results show that there are sharp vibrations for NWTC in the process of start-up and shut-down. And the time needed for the water transport balance increases with the increase in the current. The balanced NWTC ranges from -0.2 to 0.2, and it increases with the increase in the operation current in the present research. In the view of flooding prevention, it is reasonable to humidify the anode inlet gas with the lower temperature than that of cathode side by decreasing the osmotic-drag water from anode to cathode. (C) 2010 Elsevier B.V. All rights reserved.