In　this　paper,　the　application　of　＇TYL＇　frame　method,　proposed　in　the　＇Precast　Segmental　Box　Girder　Bridge　Manual＇,　is　extended　to　box　girder　with　cantilevers.　For　structural　analysis,　the　calculating　formulas　of　the　method　proposed　are　derived.　From　the　comparison　of　the　calculated　results　by　the　extended　＇TYL＇　method　with　those　by　the　high　order　finite　stripe　method　and　the　measured　results　in　model　test,　we　can　draw　the　conclusion　that　the　extended　＇TYL＇　method　is　accurate　enough　and　quite　simple　and　convenient　for　structural　design.