To　protect　Chinese　ancient　building,by　theoretical　calculation　and　finite　element　simulation　sinkage　as　well　as　strengthening　method　on　tenon-mortise　joint　of　a　face　beam　in　Tai-He　Palace　in　the　Forbidden　City　were　studied.2　strengthening　methods　were　considered,by　calculation　diagrams　as　well　as　finite　element　models　for　the　beam　were　built　and　static　analysis　were　carried　out.Based　on　analysis　results,displacement　as　well　as　stress　distributions　of　the　face　beam　before　strengthened　were　obtained;Based　on　laws　of　cultural　relics　protection,the　2　strengthening　methods　were　discussed　and　the　more　suitable　one　was　selected.Results　show　that　the　main　cause　of　sinkage　of　the　face　beam　tenon　relates　closely　to　over　great　values　of　bending,tension　as　well　as　shearing　stress　values　at　the　tenon-mortise　joint　position;The　method　that　strengthening　tenon-mortise　joint　by　additional　columns　under　the　face　beam　may　bring　adverse　effects　to　the　substructure,however　the　method　of　using　steel-wood　composite　system　to　strengthen　the　joint　is　more　suitable　which　meets　the　demand　of　cultural　relics　protection.