The effects of different operating parameters on humidification and cooling for proton exchange membrane fuel cells (PEMFCs) using direct water injection method were experimentally investigated. Experiments with various injection water temperature, operating pressure and relative humidity of cathode side were carried out. In order to quantitatively analyze the performance of direct water injection method, polarization curves and dew point temperatures of cathode outlet gas were measured. Also, the possible mechanisms of the effect of each parameter were discussed. The experimental results showed that elevation of the injection water temperature and relative humidity of cathode side led to the improvement of stack performance. It resulted from humidification and cooling effect by the evaporation of injected water. Operating pressure also had an effect on the performance of direct water injection method. In pressurized operating condition, the evaporation of injected water was difficult to occur, and the effect of direct water injection method decreased. Based on the experimental results, it was demonstrated that the stack performance was remarkably improved because of humidification and cooling effect from direct water injection method. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.