In　this　paper,　we　study　the　local　behavior　of　positive　solutions　near　the　boundary　singularity　to　the　fourth　order　Lane-Emden　equations.　By　a　blow-up　analysis　and　the　Liouville　theorem,　we　derive　an　upper　bound　and　the　boundary　Harnack　inequality.　Then　we　establish　a　generalized　B　&　ocirc;cher　theorem　and　give　a　classification　of　the　boundary　isolated　singularity.