Abstract: The high density polyethylene (HDPE) with three different molecular weight were blended with linear low density polyethylene (LLDPE) to improve the tensile strength and modulus of LLDPE and expand its application field, and then molded by micro-injection molding to prepare HDPE-LLDPE parts. A combination of DSC, wide-angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS) and tensile test were performed to provide a comprehensive analysis of microstructure variations and mechanical properties. The tensile test indicates that the tensile strength and modulus of micro-injection molded HDPE-LLDPE parts are enhanced compared with the pure LLDPE. The microstructure characterizations show that the macromolecular and lamellar orientation degree and crystallinity of HDPE-LLDPE increase with increasing molecular weight of HDPE and more highly oriented structure, Shish-Kebab, is formed in HDPE-LLDPE composites. The reasons for considerably enhanced tensile strength and modulus are elucidated based on the analysis of microstructural results.