In　order　to　protect　Chinese　ancient　buildings,　numerical　simulation　is　used　to　study　damage　types　of　tenon-mortise　joints　of　Chinese　ancient　wooden　buildings　under　bending　loads.　Two　typical　tenon-mortise　joints　are　selected　for　simulation:　Straight　joint　and　Yan-wei　joint.　By　ANSYS　program　finite　element　models　of　the　two　tenon-mortise　joints　are　built.　By　applying　displacement　load　on　side　face　of　beam　(10mm　upward)　step　by　step　status　of　tensile　stress,　compression　stress,　shearing　stress　and　moment-rotation　angle　relationship　of　the　two　joints　are　studied.　Peak　values　of　stresses　above　at　each　step　of　both　joints　are　obtained.　Results　show　that　for　a　Straight　joint　under　bending　loads　damage　types　of　its　tenon　include　tensile　strength　failure.　compression　strength　failure　and　shearing　strength　failure;　However　its　mortise　will　not　be　damaged:　For　a　Yan-wei　joint　both　the　tenon　and　mortise　will　be　damaged　for　tensile　strength　failure,　compression　strength　failure　and　shearing　strength　failure;　On　the　other　hand,　rotation　stiffness　of　Yan-wei　joint　is　larger　than　that　of　Straight　joint,　which　means　the　Yan-wei　joint　is　hard　to　be　rotated,　and　once　it　is　rotated,　it　is　more　likely　to　be　damaged.