AbstractFor the porous‐membrane‐based osmotic energy generator, the potential synergistic enhancement mechanism of various key parameters is still controversial, especially because optimizing the trade‐off between permeability and selectivity is still a challenge. Here, to construct a permeability and selectivity synergistically enhanced osmotic energy generator, the two‐dimensional porous membranes with tunable charge density are prepared by inserting sulfonated polyether sulfone into graphene oxide. Influences of charge density and pore size on the ion transport are explored, and the ionic behaviors in the channel are calculated by numerical simulations. The mechanism of ion transport in the process is studied in depth, and the fundamental principles of energy conversion are revealed. The results demonstrate that charge density and pore size should be matched to construct the optimal ion channel. This collaborative enhancement strategy of permeability and selectivity has significantly improved the output power in osmotic energy generation; compared to the pure graphene oxide membrane, the composite membrane presents almost 20 times improvement.