Nanofluidics is promising in the construction of highly-efficient osmotic energy generator, but it is still a challenge to develop large-scale and highperformance nanofluidic membranes. The emerging covalent organic frameworks (COFs) provide a desirable platform to create nanofluidic membranes with high ion selectivity and permeability towards effective osmotic energy conversion. Herein, an ultrathin self-standing COF nanofluidic membranes based on terephthalaldehyde-tetrakis(4-aminophenyl)methane is developed to construct high-efficiency nanofluidic osmotic energy generator. Benefiting from the nano-confined channels (1.4 nm) and negative surface charges, the COF based nanofluidic membrane demonstrates both excellent cation selectivity and high ion conductance. Moreover, an ultrathin thickness of ≈1.5 µm significantly reduces the membrane resistance. Consequently, the nanofluidic osmotic energy generator based on COF membrane can deliver a high output power of 5.31 W m −2 under a 50-fold salinity gradient simulating natural river/ sea junction, which is superior to most reported systems and reaches the industrial level. More importantly, such a COF nanofluidic membrane exhibits excellent stability in response to various environmental factors, including wide saline solution concentration, temperature and pH ranges. This work is anticipated to highlight the great potential of 1D COF nanofluidic membranes toward highly-efficient osmotic energy generators.