A　three-dimensional　model　of　an　elasto-plastic　rough　surface　featured　by　fractal　geometry　sliding　over　an　elasto-plastic　flat　body　is　developed.　The　three-dimensional　model　considers　the　thermo-mechanical　coupling　and　the　heat　flux　coupling　between　the　sliding　surfaces.　To　obtain　the　transient　real　contact　area,　the　problem　under　this　three-dimensional　model　is　solved　by　the　finite　element　method.　The　results　show　that　the　real　contact　area　is　a　small　fraction　of　the　nominal　contact　area　during　the　loading　and　sliding　process,　and　increases　with　the　increase　in　the　applied　normal　load.　In　the　initial　stage　of　friction　sliding,　the　real　contact　area　increases　and　fluctuates　noticeably　for　the　abrupt　change　of　sliding　speed,　and　then　varies　in　a　small　range　under　the　constant　normal　load　and　sliding　velocity.　It　is　also　shown　that　frictional　heating　increases　the　real　contact　area,　the　instantaneous　maximum　contact　pressure　by　comparing　the　results　with　those　obtained　from　the　same　model,　however,　in　which　the　thermal　effect　of　frictional　heat　is　not　considered.　That　is　to　say,　the　real　contact　area　is　larger　when　the　thermo-mechanical　coupling　is　considered.　It　is　crucial　to　take　the　thermo-mechanical　coupling　effect　into　account　especially　for　the　micro　frictional　sliding　analysis.