Abstract: Alkali lignin and coffee shell powder were researched as raw materials in this paper, and wood plastic composites (WPC) were prepared by alkali lignin, coffee shell powder, eucalyptus powder, high density polyethylene (HDPE) and additives through melt mixing, extrusion granulation and hot compression molding. The effects of alkali lignin and coffee shell powder on the mechanical properties, water absorption, dynamic thermal mechanical properties of WPC samples were studied as well, and the main chemical components of coffee shell powder were analyzed. The results showed that the main chemical composition of coffee shell powder was similar close to eucalyptus wood powder. Both the bending strength and tensile strength firstly increased and then decreased with the increasing of lignin content for the lignin group. Whereas, the mechanical properties of WPC samples prepared by alkali lignin and coffee shell powder were significantly improved, with the bending strength was increased by 49.31%, and impact strength was enhanced by 16.62%. The WPC samples prepared by alkali lignin and coffee shell powder displayed good compatibility and a desired uniform interior morphology, contributed to better thermal stability. Through observation on morphology of the fracture surface, it could be concluded that more compact and uniform interface bonding layer, which showed a more preferable interface bonding. Furthermore, the decay resistance against fungi of WPC samples was improved with the lignin addition, and the samples prepared by coffee shell powder and alkali lignin had preferable decay resistance against decay fungi compared with samples prepared with only lignin. Through multi-analysis of experimental results, the optimum formulation was proposed that the addition amount of alkali lignin was 15%, correspondingly the addition amount of coffee shell powder was 45%.