To　improve　the　disaster　prevention　and　mitigation　of　metro　shield　tunnel,　model　test　of　similar　material　and　numerical　calculation　is　studied　in　this　paper　to　simulate　the　construction　of　building　adjacent　to　foundation　pit　in　Beijing.　Under　unloading-loading　conditions　of　the　foundation　pit　above,　the　mechanical　characteristics　of　shield　tunnel　are　studied,　and　the　influence　of　spacing　between　the　bottom　of　the　foundation　pit　and　the　shield　tunnel　top　and　the　loading　strength　of　foundation　pit　are　also　analyzed.　As　shown　by　calculation,　in　unloading　stage,　the　vertical　displacement　of　shield　tunnel　gradually　increases.　When　the　foundation　pit　is　excavated　to　the　bottom,　the　vertical　displacement　reaches　the　maximum　value.　Under　loading　condition,　the　vertical　displacement　of　shield　tunnel　can　be　restored.　The　greatest　impact　on　shield　tunnel　always　occurs　at　the　end　of　the　foundation　excavation.　At　this　point,　the　work　of　foundation　slab　construction　should　be　completed　as　soon　as　possible.　In　the　unloading-loading　process　of　foundation　pit,　earth　pressure　of　shield　tunnel　presents　calabash　type　symmetrical　distribution.　At　the　top　and　bottom　of　the　shield　tunnel　the　earth　pressure　is　larger　than　the　soil　pressure　in　the　middle　of　the　shield　tunnel.　In　unloading　stage,　the　earth　pressure　of　shield　tunnel　vertical　axis　was　significantly　reduced.　In　loading　stage,　the　earth　pressure　of　shield　tunnel　can　be　restored.　With　the　spacing　between　the　bottom　of　foundation　pit　and　shield　tunnel　top　increases,　the　displacement　of　shield　tunnel,　the　displacement　difference　between　arch　bottom　and　arch　and　the　horizontal　convergence　are　incrementally　reduced.　When　the　spacing　greater　than　3　times　of　the　depth　of　deep　excavation,　the　additional　deformation　of　shield　tunnel　caused　by　foundation　pit　unloading-loading　effect　is　slightly.　When　the　loading　strength　of　foundation　pit　2　times　than　the　unloading　strength,　the　vertical　displacement　of　shield　tunnel　can　be　restored　to　its　original　state.　©　2018,　Science　Press.　All　right　reserved.