To　ensure　the　construction　safety　and　determine　the　safety　redundancy　of　the　envelope　structure,　a　three-dimensional　refined　numerical　model　based　on　the　modified　Cambridge　model　is　established　based　on　a　metro　station　foundation　pit　engineering　constructed　by　covering　top-down　method　in　Beijing,　China.　On　the　basis　of　verifying　the　rationality　of　the　numerical　model　by　the　data　measured　in　the　field,　the　thickness　of　the　underground　diaphragm　wall　and　the　floor　slab　and　the　diameter　of　the　column　are　changed.　The　influence　of　the　change　of　the　parameters　of　the　envelope　structure　on　the　deformation　of　the　foundation　pit　and　the　change　of　the　redundancy　against　continuous　damage　are　analyzed.　The　results　show　the　following:　(1)　The　coupling　effect　of　the　space　effect　and　the　pit　angle　effect　of　the　foundation　pit　leads　to　the　distribution　rule　of　the　maximum　horizontal　displacement　value　of　the　underground　diaphragm　wall:　the　horizontal　displacement　value　of　the　middle　underground　diaphragm　wall　of　the　long　side　of　the　foundation　pit　is　the　largest,　the　horizontal　displacement　value　of　other　positions　is　relatively　small,　and　the　horizontal　displacement　value　of　the　underground　diaphragm　wall　of　the　short　side　of　the　foundation　pit　is　the　smallest.　(2)　As　the　thickness　of　the　underground　diaphragm　wall　and　floor　becomes　smaller,　the　horizontal　displacement　value　of　the　deep　layer　of　the　underground　diaphragm　wall　gradually　increases,　and　the　change　of　the　maximum　horizontal　displacement　value　of　the　underground　diaphragm　wall　increases　exponentially;　the　surface　subsidence　value　increases　gradually,　surface　settlement　mainly　occurs　in　the　range　of　2　times　the　depth　of　the　foundation　pit,　and　the　surface　settlement　in　the　range　of　2~4　times　the　depth　of　the　foundation　pit　is　no　longer　significant.　(3)　The　stiffness　of　the　floor　in　the　covering　top-down　method　is　greater　than　that　of　the　inner　support　in　the　open-cut　method,　and　the　resistance　to　deformation　is　stronger,　but　the　horizontal　deformation　of　the　envelope　structure　is　still　affected　by　the　geological　conditions　and　structural　materials　to　a　certain　extent.　(4)　When　the　thickness　of　the　underground　diaphragm　wall　and　the　floor　reaches　1.0　m,　the　redundancy　of　the　vertical　envelope　structure　tends　to　be　stable,　and　the　continuous　increase　of　the　thickness　of　the　underground　diaphragm　wall　and　the　floor　will　not　increase　the　ability　of　the　structure　to　resist　continuous　damage.　©　2023　The　Author(s).