Electron backscatter diffraction (EBSD) has been developed as a novel technique for characterizing crystallographic textures in recent years. The present paper proposes an “in-situ-tracking” approach using SEM and EBSD to examining the microstructural development and grain boundary variation of stainless steel during elevated 1200 °C service. The results revealed that in addition to the coarsened grains the fraction of low angle grain boundaries (LABG) became increased and flattened obviously during service. Comparing to the regular high temperature service (below 900 °C), the present “recovery and recrystallization” process was accelerated due to dislocation fastened movement and intensive interaction. However, the grain growth mechanism still meet the well-accepted dislocation model of subgrain combination.