<p>Developing artificial membranes with stable and uniform angstrom-scale channels that can effectively reject hydrated ions is a substantial challenge but important in water desalination and energy conversion/storage applications. Achieving precise water/ions separation while maintaining high water flux requires a membrane microstructure engineered with molecular precision. This study reports the successful synthesis of ultra-thin, centimetre-scale graphdiyne (GDY) films with ordered one-dimensional (1D) channels using single-crystalline Cu (111) as the growth substrate and demonstrates their exceptional performance as molecular sieves for highly efficient water/ion separation. The optimized membrane exhibits an ultra-high water/NaCl selectivity of 5.96 × 10⁴, outperforming state-of-the-art membranes, at a water permeance of ∼32.9 mol m⁻² h⁻¹ bar⁻¹ and a salt rejection exceeding 99.7% for small ions in seawater. Mechanism studies reveal that the hydrophobic angstrom-scale channels in GDY crystals force water molecules into a single-file configuration with 1D hydrogen bond during water permeation. The 1D water chain enables the GDY membrane to facilitate rapid (diffusion constant as high as 1.3 × 10⁻⁴ cm² s⁻¹) and selective proton transport via the Grotthuss mechanism. This work contributes to the development of carbon nanomaterial membranes for precise molecular sieving and biomimetic protonophores.</p>