AbstractReverse electrodialysis is a promising method to harvest the osmotic energy stored between seawater and freshwater, but it has been a long‐standing challenge to fabricate permselective membranes with the power density surpassing the industry benchmark of 5.0 W m−2 for half a century. Herein, a vertically transported graphene oxide (V‐GO) with the combination of high ion selectivity and ultrafast ion permeation is reported, whose permeation is three orders of magnitude higher than the extensively studied horizontally transported GO (H‐GO). By mixing artificial seawater and river water, an unprecedented high output power density of 10.6 W m−2 is obtained, outperforming all existing materials. Molecular dynamics (MD) simulations reveal the mechanism of the ultrafast transport in V‐GO results from the quick entering of ions and the large accessible area as well as the apparent short diffusion paths in V‐GO. These results will facilitate the practical application of osmotic energy and bring an innovative design strategy for various systems involving ultrafast transport, such as filtration and catalysis.