Underpinning　is　a　new　concept　summed　up　from　engineering　practice　in　recent　years;　its　principle　is　based　on　the　relative　position　(distance)　between　the　excavation　and　the　existing　buildings,　the　weight　of　buildings,　soil　engineering　property,　the　probable　destroy　type　and　extension,　with　the　load　transfer　and　the　stress　transfer　theory　as　the　guiding　ideology;　designing　to　use　less　underpinning　component　to　attain　the　purpose　of　anti-lean.　The　finite　element　analysis　software　package,　Plaxis　ver7.2,　is　used　to　study　the　underpinning　excavation　engineering.　The　anchor　dead　pressure　piles　are　used　to　underpin　the　existing　structure;　and　the　finite　element　simulation　is　used　to　study　the　effect　of　underpinning　on　the　force　and　deformation　of　the　bracing　structure.　Through　finite　element　analysis,　it　can　be　found　that　the　distance　between　the　excavation　and　the　existing　buildings　and　the　thickness　of　the　weak　layer　are　important　factor　to　underpinning.