Abstract: Lignin(Lig) and a flame retardancy of P-N-B were added to wood flour/high density polyethylene (WF/HDPE)mixture alone or in combination to prepare Lig-WF/HDPE composites by extrusion. The role of Lig in Lig-WF/HDPE composites flame retardation was investigated. The results of cone calorimeter show that Lig can effectively reduce the heat release rate of Lig-WF/HDPE composites and increase the quantity of residues. The flame retardant capacity of Lig-WF/HDPE composites is optimum when Lig is added at 15wt% level, however, the total smoke production is high. When Lig and flame retardancy of P-N-B are added together, the smoke release of (P-N-B)-Lig-WF/HDPE composites is obviously reduced and the flame retardancy is furthermore improved. When the Lig is 5wt% and flame retardancy of P-N-B is 10wt%, the limiting oxygen index of (P-N-B)-Lig-WF/HDPE composite increases from 24.3 to 27.3 when flame retardancy of (P-N-B) and Lig is not added. In addition, the combination of Lig and flame retardancy of P-N-B improves the mechanical properties of (P-N-B)-Lig-WF/HDPE composites comparing to using them separately.