Plastic　deformation　behavior　of　Inconel　740H　superalloy　during　uniaxial　tension　at　high　temperature　was　investigated.　The　self-developed　in-situ　high-temperature　tensile　stage　provides　a　better　method　for　the　study　of　tensile　deformation　of　materials　under　different　conditions.　By　a　joint　application　of　in-situ　SEM　and　EBSD　techniques,　the　tensile　mechanical　properties,　microstructure,　orientation,　and　grain　boundary　evolutions　under　near-service　conditions　(650　degrees　C)　were　experimentally　investigated.　The　results　obtained　show　that　due　to　the　different　grain　orientations　of　polycrystalline　metals,　the　grains　with　preferable　orientation　begin　to　slip　first　under　the　external　force,　while　those　orientation　of　harder　grains　will　slip　until　they　rotate　to　favorable　orientation.　In　order　to　ensure　the　continuity　of　the　matrix,　the　deformation　between　grains　must　be　coordinated.　Meanwhile,　in-situ　observation　of　the　grain　rotation　at　high　temperature　shows　that　rotation　angles　and　paths　of　different　grains　are　related　to　the　initial　orientation.　By　tracing　typical　grains　and　analyzing　the　grain　rotation　during　in-situ　EBSD　testing,　it　was　found　that　some　grains　with　randomly　distributed　orientation　at　the　initial　state　gradually　changed　to　the　direction　between　[001]　and　[111]　poles　with　the　stress　increasing.　This　complies　with　the　overall　trend　of　a　single　grain　rotation.　However,　after　that　the　grains　tend　to　reach　the　[101]　pole　rather　than　the　stable　orientation　[112].　During　the　total　deformation　process,　low-angle　boundaries　form　and　accumulate　at　the　grain　boundaries　with　concentration　of　stresses.　While　high-angle　boundaries　are　slightly　affected　by　the　tensile　deformation,　and　the　density　of　twin　boundary　(TB)　decreases.　(C)　2019　Elsevier　B.V.　All　rights　reserved.