In　order　to　provide　theoretical　references　for　detection　of　structural　status　in　civil　engineering,　this　paper　proposed　a　novel　structural　non-linearity　detection　strategy　based　on　the　discrete　wavelet　transform(DWT)and　null　space　method.　Firstly,　the　structural　response　was　separated　by　DWT　to　obtain　the　approximate　signal　in　low　frequency　band.　Then,　the　obtained　approximate　signals　were　used　to　construct　a　Hankel　matrix,　which　was　decomposed　by　singular　value　decomposition(SVD)to　divide　the　null　and　non-null　spaces.　Finally,　two　new　index,　theta　and　DON,　were　proposed　to　detect　the　non-linearity;　furthermore,　a　limit　of　linearity(LL)was　constructed.　A　numerical　example　and　a　laboratory　test　were　conducted　to　verify　effectiveness　of　the　proposed　method.　Results　show　that　theta　is　significantly　less　than　its　LL　and　DON　is　almost　equal　to　1　when　the　structure　is　linear;　in　contrast,　when　the　structure　is　nonlinear,　both　theta　and　DON　are　significantly　larger　than　their　LL　and　increase　with　the　degree　of　non-linearity.　Conclusion　is　that　the　proposed　method　is　able　to　effectively　detect　the　structural　non-linearity,　furthermore,　the　proposed　method　has　excellent　robustness　and　engineering　practicability.　©　2016,　Editorial　Department　of　Journal　of　SJZU.　All　right　reserved.