The aim of this work was to provide theoretical support for material modification from the aspect of microstructure. Based on EVOH with good barrier property, blending of EVOH with PP or HDPE resulted in the formation of EVOH/PP and EVOH/HDPE. On this basis, Materials Studio 5.0 computer molecular simulation software was applied to construct molecular dynamics model for the packaging material under high pressure processing (HPP), while Discover Analysis and Amorphous Cell Analysis were used respectively to calculate the concentration profile of oxygen within the mixed crystal cells of EVOH, EVOH/PP and EVOH/HDPE and the corresponding cohesive energy density (CED). The oxygen permeability of EVOH/PP and EVOH/HDPE was significantly weakened. EVOH, EVOH/PP and EVOH/HDPE had 2 dotted line peaks,1 dotted line peak and 1 dashed line peak respectively in the range of 1.2~1.4 nm under 800 MPa. The CED of EVOH, EVOH/HDPE and EVOH/PP increased with the increasing pressure of HPP, increasing from 276.2 J/m3 (0.1 MPa) to 340.344 J/m3 (800 MPa) for EVOH/HDPE, from 70.8 J/m（ 3 0.1 MPa） to 240.5 J/m（ 3 800 MPa）for EVOH/PP. The CED values of EVOH/HDPE and EVOH/PP were both lower than that of EVOH. In conclusion, HPP affected the microstructure of the selected packaging material and thus its barrier and mechanical properties.