The operating temperature of proton exchange membrane fuel cell (PEMFC) is only at 60∼70 °C. The water and thermal management have important roles in the fuel cell. Especially the water management, it can make fuel cell operate at optimal performance, and avoid drying and flooding phenomenon. This paper discusses the effects of humidification and temperature difference of anode and cathode to the water transport phenomenon in the PEMFC. By the mixing effects of electro-osmosis and back diffusion phenomenon in the membrane, it is hard to distinguish which one determines the major water transport. This paper aims to understand the determining effect of the two phenomena in high constant current density. The results show that electro-osmosis and back diffusion are greatly influenced by temperature difference. When the temperature of cathode is higher than anode, the electro-osmosis effect is suppressed and the water transport to cathode through membrane is low. On the contrary, when the temperature of cathode is lower than anode, the electro-osmosis effect is enhanced and the water transport to cathode through membrane is high. The back diffusion has the same trend with electro-osmosis. The effect is as obvious as the increase of the temperature difference between the membrane. With this tendency, we can control the water transport direction by change the temperature of inlet gas to manage the water balance of the fuel cell without cutting off the load.