Abstract: Pulp and paper industry waste (PIW) was used to fill high density polyethylene (HDPE) to prepare PIW/HDPE composites, the water absorption, thermal, flame retardant, tensile and dynamic mechanical properties of PIW/HDPE composites were tested and analyzed by water bath box, thermal deformation Vicat temperature tester, oxygen index meter, electronic universal testing machine and dynamic thermomechanical analyzer. The results show that PIW/HDPE composites have good bonding interface and tensile properties, the best tensile strength is 23.18 MPa, the increment of PIW is negative to the water absorption and toughness of PIW/HDPE composites, but the increment of PIW improves the thermal property, flame retardant property (the highest oxygen index is 29.98%) and rigidity of PIW/HDPE composites. The results of this study can provide useful experience for the utilization of PIW.