The　health　monitoring　and　damage　detection　of　structures　are　major　scientific　issues　that　the　civil　engineering　discipline,　which　made　great　achievements　in　the　20th　century,　has　bequeathed　to　the　21st　century.　Despite　the　installation　of　health　monitoring　systems　in　many　large　structures,　implementing　damage　detection　through　finite　element　model　updating　is　often　time-consuming　or　even　infeasible　due　to　the　size　of　the　model　and　the　presence　of　numerous　uncertain　parameters.　To　address　this　issue,　this　paper　proposes　a　substructure-based　model　updating　method.　The　entire　structure　is　divided　into　substructures　with　reduced　degrees　of　freedom,　allowing　for　the　simplification　of　the　motion　equation　by　employing　only　a　small　number　of　low-order　modes　from　each　substructure.　Consequently,　the　analysis　scale　of　the　structure　is　effectively　reduced.　The　discarded　higher　modes　are　compensated　by　residual　modes　to　ensure　the　accuracy　of　structural　response　and　sensitivity.　Subsequently,　a　damage　identification　program　substructurebased　model　updating　is　developed,　which　is　applied　to　component　mode　synthesis　and　damage　identification　for　large　structures.　By　precisely　detecting　damage　in　critical　areas,　accurate　diagnosis　and　evaluation　of　the　global　structural　safety　are　achieved.　The　results　validate　the　implementation,　computational　efficiency,　and　accuracy　of　the　proposed　substructure-based　model　updating　method.　This　approach　shifts　the　focus　from　model　updating　of　the　entire　structure　to　model　updating　of　substructures,　with　the　aim　of　fundamentally　resolving　the　technical　challenge　of　accurate　damage　detection　of　large　and　complex　structures.　Furthermore,　it　provides　theoretical　support　for　the　practical　application　of　damage　detection　in　large　civil　structures.