Covalent organic framework (COF) membranes are promising for water treatment applications owing to their uniform pores and outstanding chemical stability. However, the harsh conditions and low synthetic efficiency of conventional solvothermal synthesis of COF membranes have severely hindered their practical development. Herein, we developed a dynamic interfacial polymerization strategy to rapidly construct a TpPa-1 selective layer on a polyacrylonitrile substrate within only 3 min. This method enabled the rapid and efficient fabrication of COF membranes by confining the reaction region to shorten the diffusion path of the monomers while exploiting the intrinsic high reactivity of TpPa-1 monomers. The rapid fabrication resulted in a thinner selective layer and enhanced permeance performance. In the methyl blue/Na₂SO₄ nanofiltration test, the separation factor reached 212, with a permeance of 865 L∙m^–2∙h^–1∙MPa^–1, outperforming most previously reported COF membranes.