Abstract: Organic nano-montmorillonite/high density polyethylene (OMMT/HDPE) composites were prepared by multistage stretching extrusion and traditional extrusion process. The morphological structure and property of the two different OMMT/HDPE composites were comparatively studied by wide-angle X-ray diffraction (WAXD), TEM, DSC, small-angle X-ray scattering (SAXS) and so on. The results indicate that multistage stretching extrusion shows great effect on refining particle size of OMMT and promoting dispersion of OMMT in HDPE matrix. With increasing of the number of layer multiplying elements (LMEs), the dispersion of OMMT is gradually improved and the length-to-diameter ratio of OMMT aggregation is also increased, leading to the enhanced initial nucleation rate and crystallization rate of OMMT/HDPE composites, inducing the formation of oriented shish-kebab structures in OMMT/HDPE composites. Accordingly, the tensile strength of OMMT/HDPE composites prepared by multistage stretching extrusion is greatly enhanced. When the mass ratio of OMMT:HDPE is 1:100 and 5:100, the tensile strength of OMMT/HDPE composites prepared by multistage stretching extrusion increases about 50% and 356% compared to that of OMMT/HDPE composites prepared by traditional extrusion process.