Salinity gradient energy is an abundant renewable energy source that can help satisfy the growing global demand for energy. Although current approaches based on membrane design for salinity gradient energy conversion have been demonstrated to improve conversion efficiency they suffer from the trade-off between selectivity and intrinsic resistance of the membranes, which impedes the rates of energy conversion. In this study, a charged porous asymmetric membrane was fabricated, consisting of a thin charged nanopore (~1 nm) layer and a charged porous structure (80–100 nm) layer. Its asymmetric electric potential and charged porous structure increase its affinity to uniport of ions and enables high ion conductivity. While maintaining a high degree of selectivity, the membrane exhibited an intrinsic membrane resistance of 0.53 ± 0.12 Ω·cm2, which was lower than that of the commercial and other reported membranes. The maximum power density reached up to 12.5 W/m2 with a 500-fold salinity gradient. This membrane shows great promise in industrialization and provides new insights into high salinity energy conversion.