Tidal　flats　in　northern　China　are　essential　parts　of　the　East　Asian-Australasian　Flyway,　the　densest　pathway　for　migratory　waterbirds,　and　are　of　great　ecological　and　economic　importance.　They　are　threatened　by　human　activities　and　climate　change,　raising　the　urgency　surrounding　tracking　the　spatiotemporal　dynamics　of　tidal　flats.　However,　there　is　no　cost-effective　way　to　map　morphological　changes　on　a　large　spatial　scale　due　to　the　inaccessibility　of　the　mudflats.　In　this　study,　we　proposed　a　pixel-based　multi-indices　tidal　flat　mapping　algorithm　that　precisely　characterizes　2D/3D　morphological　changes　in　tidal　flats　in　northern　China　using　time-series　remote　sensing　data.　An　overall　accuracy　of　0.95　in　delineating　tidal　flats　to　a　2D　extent　was　achieved,　with　11,716　verification　points.　Our　results　demonstrate　that　the　reduction　in　sediment　discharge　from　rivers　along　the　coastlines　of　the　Yellow　and　Bohai　Seas　has　resulted　in　an　overall　decline　in　the　area　of　tidal　flats,　from　4856.40　km2　to　4778.32　km2.　Specifically,　3D　analysis　showed　that　significant　losses　were　observed　in　the　mid-to-high-tidal　flat　zones,　while　low-elevation　tidal　flats　experienced　an　increase　in　area　due　to　the　transformations　in　mid-to-high-tidal　flats.　Our　results　indicate　that　the　sediment　inputs　from　rivers　and　the　succession　of　native　vegetation　are　the　primary　drivers　leading　to　2D/3D　morphological　changes　of　tidal　flats　following　the　cessation　of　extensive　land　reclamation　in　northern　China.　©　2024　by　the　authors.