An economical and highly uranium extraction from seawater remains a crucial task for energy sources and environmental safety. Aiming for improving mass transfer rate of uranium adsorption from seawater, a new synthetic strategy was adopted for the fabrication of 2D-open channel microporous bio-adsorbent for uranium extraction from seawater. Herein, the in-situ ATRP grafting approach was adopted to graft divinylbenzene, polyacrylonitrile onto the surfaces of microporous frameworks via the vapour phase method. The post-synthetic functionalization was carried out by hydrothermal method, where amidoxime groups are structure-directing agents to trap uranium. Further, amidoxime groups not only enhanced hydrophilicity but also adjusts adsorbents pKa. AO-Fc faces minimum interference of competing ions and achieves a high uranium adsorption capacity of 8.57±0.02 and 409±1 mg/g in seawater and simulated solution. Despite its stable structure, AO-Fc exhibits a long life span and negligible weight loss revealed AO-Fc could be applied as a potential adsorbent for radionuclide.