Osmotic energy conversion (OEC) is attractive for salinity-gradient power utilization. Nevertheless, the OEC still faces a challenge of relatively low power density owing to the limited ionic mass transfer. In this paper, we present designed interfacial nanostructures (DINS) to enhance ion selective transport in nanopores. The maximum osmotic power under 50-fold salt concentration ratio is ameliorated by 180.6%, when DINS are applied in nanopore region. When DINS are partially applied at low salt concentration side rather than high salt concentration side, the maximum osmotic power under 50-fold salt concentration ratio is enhanced by 139.1%. Once the temperature of aqueous solution at low salt concentration side with high original electric double layer thickness is raised up, the maximum osmotic power under 50-fold salt concentration ratio is consolidated by 19.8%. Therefore, a principle “Strengthening the electric double layer with high original thickness adjacent to low salt concentration reservoir” is constructed for enhancing OEC performance. Besides, when temperature difference between two reservoirs with artificial seawater and freshwater is varied from 35 °C to −35 °C, the experimental osmotic power density is consolidated from 3.09 W/m2 to 4.78 W/m2 by 54.7%. The current work offers a principle to improve OEC performance with DINS under thermal modulation.