The　deflections　of　retaining　structures　during　deep　excavation　should　be　controlled　below　a　predefined　threshold　in　an　attempt　to　mitigate　the　deformation-posed　damage　to　the　surrounding　buildings　and　infrastructure　facilities.　In　this　paper,　a　new　approach　is　presented　to　conducting　deformation　reliability　assessments　of　retaining　structures.　The　method　is　based　on　an　extension　of　the　classical　first-passage　reliability　problem　and　is　applied　on　the　spatial　scale　of　the　retaining　structures.　With　the　proposed　method,　the　in　situ　monitoring　data　and　the　associated　measurement　error　can　be　easily　incorporated,　which　accordingly　improves　the　assessment　accuracy.　Moreover,　the　proposed　method　has　a　closed-form　solution,　which　is　beneficial　for　the　computation　efficiency　and　its　practical　application.　The　method　was　applied　to　assess　the　retaining　structure　reliability　in　a　foundation　excavation　of　a　subway　station　in　Fuzhou,　China.　The　accuracy　of　the　analytical　results　was　verified　through　a　comparison　with　those　of　Monte　Carlo　simulation.　It　was　shown　that　the　proposed　method　can　represent　well,　the　deformation-based　safety　level　of　retaining　structures.　©　2019　by　the　authors.