This　paper　proposes　a　three-dimensional　analytical　model　of　blow-out　for　a　shallow　tunnel　in　sand.　Upper　bound　theorem　is　adopted　to　deduce　the　analytical　solutions　of　limit　support　pressure,　and　a　dimensionless　parameter　called　partial　failure　ratio　is　defined　to　describe　the　range　of　partial　failure　within　the　tunnel　face.　A　series　of　numerical　simulations　are　carried　out　to　analyse　the　limit　support　pressure　and　failure　zone　on　the　limit　conditions.　Finally,　the　analytical　solutions　including　the　partial　failure　ratio　and　limit　support　pressure　obtained　by　the　proposed　model　are　compared　with　those　obtained　by　the　numerical　simulation　and　the　existing　global　failure　model　approaches.　Results　show　that　the　proposed　model　in　this　paper　can　not　only　analyze　the　partial　failure　with　better　accuracy,　but　can　also　consider　the　global　failure.　The　proposed　model　has　more　extensive　applicability　in　analyzing　the　face　stability　of　blow-out　for　a　shallow　shield　tunnel.