In proton exchange membrane fuel cell (PEMFC), pressure drop at cathode can be used in water management. However, the equation to determine the cathode two-phase-flow pressure drop online and in real time has not been reported. This paper aims to develop a novel approach to calculate this pressure drop. The originalities are the fact that cathodic pressure drop actually experiences two jumps as it rises through two levels during flooding process and the proposal of spatial average water film to determine the pressure drop online. Firstly, the equation to calculate the pressure drop of cathode single-phase flow, covering all operating conditions, is proposed and is verified at a 10 kW fuel cell stack. Secondly, we find that there exists a steady two-phase-flow pressure drop linked to an equivalent film flow in unit channel and put forward a novel approach to determine this pressure drop. Finally, water management strategy based on pressure drop is applied to a 34 cm(2) fuel cell and the voltage drop rate decreases by 35%, from 72 mV/h down to 47 at a low cathode stoichiometric ratio 2.0 in long time operation, and the parasitic consumption is reduced by up to 50%. Hence, this strategy is shown to be effective in avoiding flooding, reducing air compressor consumption and extending the running time of single operation and the lifetime of fuel cell. This paper will contribute to the conimercialization of fuel cells. (C) 2017 Elsevier Ltd. All rights reserved.