As the characteristic of forward osmosis microbial fuel cells (OsMFCs), water flux is crucial for improving electricity generation, and the ohmic resistance of the membrane itself directly influences the performance of OsMFCs. This paper was aimed at analyzing the relevance between water content and resistance of membrane on the basis of electro-osmotic and osmotic water flux which were measured respectively under the electric field and osmotic pressure in OsMFCs and explained the phase transition of intramembrane environment from non-conductive zone to the conductive zone was an important reason leading to the reduction of membrane impedance. In the meantime, the changes inner membrane structure and membrane resistance under the influence of membrane water content were also analyzed.