The　case　study　presented　is　based　on　a　new　shield　tunnel　approaching,　which　is　close　to　an　existing　subway　tunnel　in　Beijing.　With　theoretical　analysis,　numerical　modeling　and　the　feedback　of　field　monitoring,　the　influences　on　the　existing　shield　tunnel　in　terms　of　longitudinal　and　transverse　displacements,　bending　moment,　and　axial　force　brought　by　the　newly　parallel　approaching　one　are　investigated.　And　it　reveals　that　there　is　the　longitudinal　effect　on　the　existing　tunnel　when　the　extremely　close　shield　moves　forward,　which　is　presented　as　the　phenomenon　of　＇early　stress　arrival　and　deformation　lagging＇.　The　study　results　verify　that　the　effectiveness　of　the　cross　steel　support　is　remarkable　and　especially　the　transverse　steel　support　makes　a　great　contribution　to　the　improvement　the　existing　tunnel　stress　state,　which　may　provide　informative　experience　for　relevant　cases.