Water management of the proton exchange membrane fuel cell is crucial to operate the fuel cell at high performance condition with longevity. Since the electrolyte membrane is required to maintain the level of water concentration, the water vapor should be supplied to the electrolyte membrane. On the other hand, the condensed water in the catalyst layer results in performance degradation. The water concentration inside the electrolyte membrane is balanced by back diffusion and electro-osmosis that transport water molecule from electrode to electrode. The water transport phenomena of the proton exchange membrane fuel cell is evaluated to understand the relation between back diffusion of water and electro-osmosis. The system simulation model is developed under Matlab/Simulink® Environment which includes dynamic fuel cell model, air supply with humidifier, hydrogen supply model, and thermal management model. The stack temperature is controlled by thermal management system while the anode gas humidification is supported by product water of electrochemical reaction. Since the amount of exit product water is determined by the activation of back diffusion and performance of membrane humidifier, it is necessary to understand consecutive process from component to component. A dynamic simulation is conducted over various load follow-up conditions.