This　paper　aims　at　proposing　a　new　failure　mechanism　to　deal　with　the　face　stability　of　deep　tunnels　in　sandy　layer.　Numerical　simulations　were　conducted　to　analyze　the　influence　of　different　variables　on　the　limit　support　pressure　and　the　failure　zone.　Based　on　the　results　of　the　numerical　simulation,　a　new　failure　mechanism　that　combined　with　the　Protodyakonov＇s　theory　and　the　multi-block　failure　mechanisms　is　proposed.　The　limit　analysis　method　is　adopted　to　obtain　the　limit　support　pressure　and　failure　zone.　Finally,　the　limit　support　pressure　and　failure　zone　derived　from　the　new　mechanism　are　compared　with　those　given　by　numerical　simulation,　previous　researches　of　limit　analysis　and　centrifugal　test.　The　results　show　that　the　new　failure　mechanism　based　on　Protodyakonov＇s　theory　is　more　reasonable　and　accurate　to　analyze　face　stability　of　deep　tunnels.