The development of nanofluidic energy harvesting system plays a fundamental role in harvesting osmotic power from Gibbs free energy within salt concentration gradient, which is considered as a future clean and renewable energy source. In this study, a silica-nanochannel based nanofluidic energy harvesting system was fabricated and its output power density could reach 705 W/m 2 under suitable KCl concentration bias which exceeded-by almost two orders of magnitude-the results obtained by previous work. The enhancement of energy harvesting was mainly ascribed to the appropriate length of nanochannel that makes a good balance between the desirable ion selectivity and the unfavorable large resistance of nanochannel. This high-performance nanofluidic energy devices could be used in a variety of applications, including power biomedical tiny devices or constructing future clean-energy recovery plants.