Achieving simultaneous high selectivity and permeability for monovalent cation separation remains challenging due to energy-intensive dehydration requirements in current rigid nanopores. Here we develop a hydration-layer-mediated sieving strategy by anchoring hydrated ions at the pore rim of a covalent organic framework monolayer to form dynamic angstrom-scale hydrapores. Ion transport is regulated via attraction and repulsion between bound and migrating ions, arising from the merging and squeezing of hydration layers, enabling precise discrimination without full dehydration. Under a concentration gradient (∆C = 1 M), the membrane exhibits selectivity of 148 for K+/Li+ and 42 for Na+/Li+ with a K+ permeance of 2 × 104 mol m−2 h−1, three orders of magnitude higher than those of state-of-the-art membranes. A low activation energy of 5.5 kcal mol−1 indicates near-frictionless transport, offering a new paradigm for monovalent cation separation.