In　this　paper,　to　monitoring　the　2-D　deformation　of　building＇s　settlement　joint,　based　on　the　testing　Macro-strain　of　long　gauge　FBG　strain　sensing　technology,　the　calculating　method　for　the　2-D　deformation　is　derived.　One　kind　of　accurate　real　time　monitoring　method　is　proposed,　and　its　reliability　and　accuracy　are　verified　in　Lab.　Furthermore,　the　proposed　method　has　been　successfully　applied　in　monitoring　the　settlement　joint　of　a　concrete　reservoir　during　underneath　pass　construction　of　shield　tunnel　in　Wuxi　subway.