Amine-functionalized covalent organic frameworks (COFs) hold great potential in diversified applications. However, the synthesis is dominated by postsynthetic modification, while the de novo synthesis allowing for direct installation of amine groups remains a formidable challenge. Herein, we develop a site-selective synthetic strategy for the facile preparation of amine-functionalized hydrazone-linked COF for the first time. A new monomer 2-aminoterephthalohydrazide (NH2-Th) bearing both amine and hydrazide functionalities is designed to react with benzene-1,3,5-tricarbaldehyde (Bta). Remarkably, the different activity of amine and hydrazide groups toward aldehyde underpin the highly site-selective synthesis of an unprecedented NH2-Th-Bta COF with abundant free amine groups anchored in the well-defined pore channels. Interestingly, NH2-Th-Bta COF exhibits dramatically enhanced iodine uptake capacity (3.58 g g-1) in comparison to that of the nonfunctionalized Th-Bta COF counterpart (0.68 g g-1), and many reported porous adsorbents, despite its low specific surface area. Moreover, NH2-Th-Bta COF possesses exceptional cycling capability and retained high iodine uptake, even after six cycles. This work not only provides a simple and straightforward route for the de novo synthesis of amine-functionalized COFs but also uncovers the great potential of amine-functionalized COFs as adsorbents in the efficient removal of radioiodine and beyond.