The development and utilization of salinity gradient energy are of great significance to the carbon-neutral strategic demand for clean energy in the new era. Conventional ion-exchange membranes have been employed to recover this wide-distributed energy by reverse electrodialysis membrane processes, however, the dense membrane structure and chemical instability limit the ionic transport in various working environments. Here, inspired by the rapid mass transport caused by the hierarchical structure of blood vessels, we employ two types of polyelectrolytes to fabricate a bioinspired three-dimensional interconnect porous membrane by simply casting-soaking, and this membrane shows great chemical stability due to the ionic crossing enhancement. The interconnected nanoporous structure and the enriched surface functional groups of the membrane render the high-performance osmotic energy conversion from different resources, including the Gibbs free energy between seawater and river water, commonly used organic solvents, and also in the solution treatment process of spent batteries. We believe this chemical-stable, nanoporous and freestanding membrane might take one more step towards practical applications and membrane technology.