The　high-temperature　mechanical　properties　of　carbon　fiber　reinforced　polyimide　resin　matrix　MT300/KH420　composites　were　studied　both　in　macro　and　micro　scale,　during　which　the　flexural　property　variation　rule　for　MT300/KH420　composites　of　laminates　with　ply　orientation　of　[0°]14　and　[±45°/0°/90°/+45°/0°2]s　were　especially　analyzed　at　temperature　ranging　from　ambient　temperature　to　500.　Research　shows　that　MT300/KH420　composite　has　good　mechanical　property　at　high　temperature.　The　flexural　strength　of　[0°]14　laminates　exhibit　a　51%　retention　at　420,　while　at　500　it　changes　little.　At　ambient　temperature,　[0°]14　laminates　exhibit　brittle　fractures　with　a　rough　facture　surface　and　crack　growth　direction　along　thickness.　As　temperature　rises,　resin　tends　to　have　a　stronger　flowability,　leading　to　a　viscoelastic　behavior,　while　failure　mainly　occurs　at　the　loading　nose.　At　500,　thermal　exposure　has　caused　the　decomposition　of　resin　matrix,　leaving　separations　between　the　bundles　of　the　oxidated　fibers.　As　for　[±45°/0°/90°/+45°/0°2]s　laminates,　the　flexural　properties　show　a　more　stable　retention　at　high　temperature.　Crack　along　45°　direction　at　outer　surfaces　as　well　as　interlamination　are　the　main　failure　modes.　At　500,　a　severe　delamination　happens.　Compared　with　matrix-dominated　laminates,　the　flexural　properties　of　fiber-dominated　ones　are　less　dependent　on　temperature.　©　2016,　BUAA　Culture　Media　Group　Ltd.　All　right　reserved.