Nanofluidics　is　promising　in　the　construction　of　highly-efficient　osmotic　energy　generator,　but　it　is　still　a　challenge　to　develop　large-scale　and　high-performance　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　approximate　to　1.5　mu　m　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.