Based on the mechanism of Tadokoro model, the dynamicelectro-mechanical response of Ionic polymer-metal composite (IPMC) has beensimulated using finite element method. Generally, the water moleculediffusion force is neglected in the most of the former numerical simulationworks. In the present paper, the influence of water diffusion resistanceforce in the process of the movement of sodium ion has been emphaticallyexplored and compared, by introducing two different governing equations:with and without consideration of water diffusion resistance force. Thewater diffusion resistance force is described as a non-linear term and thecorresponding governing equation is solved by iteration. The numericalresults show that the water diffusion force has no obvious effect on thedisplacement, but significant effect on the sodium ion concentration,effective moisture distribution and internal balance force. In addition, theeffect exhibits the area selection, especially at the region close to theanode and cathode. The predicting accuracy will be improved by involvingthis nonlinear component within the governing equation.