There is growing interest in harnessing energy from salinity gradients because it is readily available in nature. However, the energy harvesting system is not a separate liquid region but a coupling of solid membrane and liquid that leads to a distinct ions transport behaviors. Here, we propose a coupling model containing membrane and fluidic domain to study the effect of dielectric membrane on energy conversion performance. The results show that the surface charge of nanopore is strongly dependent of solution property (ion concentration and pH) and membrane property. The dielectric membrane promotes the surface charge and electrostatic interaction that enhances the energy conversion performance. Such enhancement is more significant at short nanopore with high concentration gradient and solution pH. The maximum output power of 2 pW and energy conversion efficiency of 42 % are obtained for single nanopore. As a proof of concept, it exhibits huge deviations if not consider the membrane and its influence on surface charge. This study provides a fresh insight on the interactions between solid membrane and solution properties in terms of energy conversion, thereby enhancing the potential for developing energy conversion devices.