This　study　investigates　crystal　orientation　evolution　at　microscopic　level,　and　changes　in　the　superconducting　properties　at　macroscopic　level　of　rare-earth-barium-copper-oxide　(REBCO)　superconductor　tape　under　severe　deformation.　At　the　microscopic　level,　in-situ　electron　backscatter　diffraction　is　used　for　real-time　observation　of　the　crystal　orientation　evolution　during　the　entire　tensile　process.　At　the　macroscopic　level,　the　critical　current　(Ic)　value　and　Ic　angle　dependence　performance　are　systematically　measured　under　different　applied　tensile　stresses.　By　comparing　the　microscopic　and　macroscopic　results,　the　synergetic　evolution　mechanism　between　them　is　successfully　established.　Stress　at　the　initial　descent　point　of　the　Ic　value　excellently　fits　the　one　where　the　(001)[100]　orientation　sharply　decreases,　thereby　revealing　the　real　Ic　degradation　mechanism　of　REBCO　tapes.　The　application　of　a　moderate　applied　tensile　stress　can　increase　the　in-field　Ic　value　and　pinning　force　because　new　generated　defects　and　strains　act　as　pinning　centers.　A　higher　tensile　stress　can　destroy　the　biaxial　texture　of　the　REBCO　layer　and　become　a　significant　barrier　to　the　supercurrent　flow.　This　research　elucidates　the　REBCO　degradation　mechanism　and　may　assist　manufacturers　in　improving　the　electromechanical　properties　of　commercial　REBCO　tape.