Large-scale　uranium　extraction　from　seawater　(UES)　is　considered　to　be　an　important　way　to　solve　the　nuclear　fuel　shortage,　and　the　development　of　highly　efficient　and　selective　adsorbents　is　a　key　factor　in　realizing　UES.　In　this　work,　Schiff　base-conjugated　amidoxime　modified　porous　organic　polymers　(OPA-PPA-AO)　were　synthesized　by　aldehyde-amine　condensation　and　hydroxylamine　reactions　for　the　adsorption　of　uranium.　OPA-PPA-AO　demonstrates　exceptional　adsorption　selectivity　and　high　adsorption　capacity,　with　an　adsorption　capacity　for　uranium　that　is　53　times　greater　than　that　for　vanadium.　The　maximal　adsorption　capacity　of　OPA-PPA-AO　reaches　316.14　mg/g.　In　real　seawater,　the　removal　rate　of　uranium　by　OPA-PPA-AO　was　63.5　%.　Mechanistic　studies　and　theoretical　calculations　showed　that　the　unique　skeletal　structure　of　OPA-PPA-AO　provided　a　suitable　structural　environment　for　the　synergistic　coordination　of　Schiff　bases　and　amidoxime　groups,　which　led　to　the　high　affinity　to　uranyl　ion.　These　results　indicate　that　OPA-PPA-AO　is　a　very　promising　material　for　uranium　extraction　from　seawater.