High density and low impact strength of traditional wood/plastic composites（WPC） present some barriers for their application in building construction.To reduce the density of WPC,the authors added a foam beater in the mixture of wheat straw and polyethylene（PE） before extrusion moulding.The effects of the wheat straw content,foam beater content,and wheat straw size on the composite performance were evaluated and presented in this study.The optimized parameters to make a low density straw and polyethylene composite were: the content ratio of polyethylene to wheat straw flour and the foam beater was 100∶30∶2,with the wheat straw flour 80,1,20 mesh size.