Before　renovation　of　Tai-he　Palace　in　the　Forbidden　City,　it　was　found　during　survey　that　some　mechanical　problems　occurred　on　its　wooden　members,　which　included:　(1)　deflection　of　middle　part　of　its　western　eave　purlin　was　overlarge;　(2)　sinkage　of　tenon　of　face　beam　in　its　3rd　part　was　overlarge;　(3)　sinkage　of　the　central　caisson　ceiling　was　obvious;　(4)　sinkage　of　tenon　of　its　side　beam　was　overlarge,　but　the　beam　had　been　strengthened　by　wooden　supports.　To　protect　Chinese　ancient　wooden　buildings,　these　problems　were　studied　by　theoretical　as　well　as　simulation　methods.　Causes　of　the　problems　as　well　as　strengthening　methods　were　also　discussed.　Results　show　that:　(1)　main　cause　for　overlarge　deflection　of　the　eave　purlin　is　aging　of　wood　material,　which　leads　to　decrease　of　elastic　modulus,　however　the　purlin　is　still　safe　enough;　(2)　overlarge　sinkage　of　tenon　of　the　face　beam　relate　closely　to　overlarge　tension,　bending　and　shearing　forces　at　the　location,　by　steel-wood　components　the　beam　can　be　effectively　strengthened;　(3)　main　cause　for　sinkage　of　the　caisson　ceiling　is　crack　of　groveling　beam　above　it,　by　iron　band　wrapping　method　the　problem　can　be　solved;　(4)　sinkage　of　tenon　of　the　side　beam　relate　closely　to　overlarge　forces　at　the　location,　by　additional　supports　the　beam　can　be　effectively　strengthened.