It has reported that the introduction of reduced graphene oxide (RGO) can enhance the crystallization and orientation of high density polyethylene (HDPE) matrix and thus improve the mechanical properties of HDPE/RGO nanocomposites. Herein, the local microstructures and orientations in different regions of HDPE/RGO bars with varied RGO contents were further explored by two dimensional small angle X-ray scattering (2D SAXS) using a microbeam technique. It is unveiled that the orientation orderings of every positions are all intensified with increasing RGO amount, and of particular interest is the observation of the quite slight change of the ordering degrees in diverse zones of HDPE/RGO nanocomposite bars, implicating that RGO imposes a uniform enhancing effect upon HDPE matrix within different areas and consequently reflects an effective increase of mechanical properties of HDPE/RGO nanocomposites.