To　solve　difficult　technology　problem　of　the　building　settlement　joint　with　two-dimension　continuous　deformation　monitoring,　the　real-time　high　precision　two-dimensional　deformation　monitoring　idea　was　proposed,　based　on　a　long　gauge　fiber　Bragg　grating　(FBG)cross　layout.　By　means　of　strict　theoretical　derivation　the　mathematical　relationship　between　the　strain　of　the　long　value　sensor　and　the　settlement　joint　deformation　was　obtained.　Using　simple　device　the　theoretical　derivation　was　tested,　and　the　error　is　very　small　to　meet　the　requirements　of　monitoring　accuracy.　Finally,　the　technology　was　applied　in　settlement　joint　monitoring　of　a　Metro　reservoir　structure　and　guidance　the　construction　correctly.　It　proves　that　the　proposed　method　has　good　reliability　and　practical　value.　©　2015,　Editorial　Board　of　Journal　of　Basic　Science　and　Engineering.　All　right　reserved.