Abstract: The high-density polyethylene (PE-HD)/waste paper (WP) and PE-HD/wheat straw (WF) composites were prepared by an injection molding method. The effects of contents of WP, WF and silane coupling agent (KH570) on the properties of the composites were investigated, and the mechanical, water absorption and interfacial properties of the composites were also analyzed comparatively. The results indicated that the mechanical properties of the composites increased first and then tended to decrease with the addition of WP and WF, and the optimum contents of WP and WF were 20 wt% nd 30 wt%, respectively. The addition of KH570 improved the interfacial compatibility and mechanical properties of the composites, but there was a decrease in water absorption performance. The optimum content of KH570 for PE-HD/WP and PE-HD/WF composites were 1 wt% and 2 wt%, respectively. The aspect ratios of WP and WF were determined as 24.2/1 and 12.5/1, respectively. When 20 wt% of WP and WF was incorporated, the mechanical properties, water absorption and interface properties of the PE-HD/WP composites were better than those of the PE-HD/WF composites.