The structural characteristics and element distribution within accessory minerals are crucial in documenting the metamorphicand deformational processes in rocks. In particular, in- situ geochronological dating of apatite has gained significant prominence, becoming vital for dating magmatic rocks and mineral deposits. Despite its significance, unresolved issues persist regarding the deformation mechanism, behavior, and restrictive impact on element diffusion in apatite during different metamorphic- deformation processes.This study focuses on rocks from the Eastern Himalayan Syntaxis, renowned for its intense tectonic deformation and metamorphism. Using SEM and CL observations, we identified notable differences inapatite within granulite and mylonitic schist. Granulite apatite lacks an apparent compositional structure, while mylonitic schist apatite exhibits distinct light and dark compositional changes. Statistical analysis of apatite distribution in thin sections revealed that the long axis of apatite grains in both metamorphic rocks aligns approximately parallel to the main foliation.Furthermore, EBSD fabric analysis unveiled clear intra- granular deformation in granulite apatite, whereas mylonitic schist apatite displayed minimal intra- granular deformation. EPMA scanning of apatite composition demonstrated a relatively uniform distribution of major elements in granulite, while silicon (Si) elements in mylonitic schist displayed evident zoning or unevenness, consistent with CL scanning results.Based on these observations, preliminary conclusions were drawn. Firstly, despite its directional distribution and intra- granular deformation, granulite apatitemay be influenced by higher metamorphic temperatures, promoting rapid element diffusion and uniform redistribution. Late- stage fluid activity metasomatized elements along low- angle grain boundaries or fractures perpendicular to maximum tensile stress. Secondly, mylonitic schist apatite, alignedwith mylonite foliation, exhibits minimal intra- granular deformation, likely due to lower deformation temperatures or the concentration of strain in quartz and mica domains, which effectively spared the relatively tough apatite from deformation. Compositional variations observed in CL images and major element distribution maps suggest limited diffusion due to lower metamorphic/deformation temperatures.Lastly, preliminary age results indicate multiple ages in granulite apatite, reflecting inherited apatite influencing element redistribution during metamorphism and late- stage metasomatism. In contrast, felsic mylonitic schist apatite records continuous fluid activity during mylonitization, leading to continuous crystallization. These findings offer valuable insights for interpreting apatite age in metamorphic and deformational rocks.