The　highly　selective　capture　of　137Cs+　from　complex　solutions　is　still　challenging　because　of　its　high　solubility,　easy　mobility,　and　the　influence　of　interfering　ions.　Here,　a　reliable　strategy　is　demonstrated　for　specific　Cs+　ion　recognition　and　separation　through　constructing　the　confined　space　as　an　＂ion　lock＂　in　the　microporous　framework.　A　new　3D　microporous　indium　oxalatophosphate　with　the　highly　selective　Cs+　capture,　namely　[Me2NH2]1.5[In2(PO4)0.5(H2PO4)(HPO4)1.5(C2O4)]　(FJSM-NINPC)　is　prepared.　FJSM-NINPC　with　excellent　radiation　resistance　shows　ultra-fast　kinetics　(high　removal　rate　of　97.63%　within　1　min)　and　high　adsorption　capacity　of　268.12　mg　g-1　for　Cs+.　It　can　highly　selectively　capture　Cs+　under　excessive　competitive　ions　and　even　in　environmental　water　samples.　Furthermore,　the　ion　exchange　column　filled　with　FJSM-NINPC　can　quickly　separate　and　recover　Cs+　from　mixed　Cs+　and　Sr2+　solution　(separation　factor　SFCs/Sr　=　249.17).　Moreover,　single　crystal　structure　analysis　combined　with　density　functional　theory　calculations　confirms　that　Cs+　ions　are　＂encapsulated＂　in　channels　of　FJSM-NINPC　by　the　suitable　spatial　confinement　and　with　strong　CsO　interactions.　This　work　not　only　provides　an　unprecedented　microporous　metal　oxalatophosphate　with　high　Cs+　selectivity　but　clearly　reveals　the　Cs+　capture　mechanism　and　structure-function　relationship　of　microporous　materials　for　radionuclides　remediation.