Natural fiber reinforced polymer composites have the advantages of low density, low cost and renewability. However, the inferior mechanical property restricts the application. In this work, EPDM-g-GMA has been added to straw/PP composites to improve the properties. The mechanical properties, thermal stability, crystallinity and melt viscosity have been invested. The results reveal that the mechanical properties of straw/PP/EPDM composites are improved remarkably and the impact strength more than doubles compared to straw/PP composites. Surface microstructure analysis reveals that the composite has good interfacial compatibility and dispersing performance. The maximum decomposition temperature, the melting enthalpy and crystallinity increased. The glass transition temperature and process ability are also improved by the addition of EPDM.