A polymeric agent acrylic acid grafted polyethylene (AAgPE) was synthesized and used as a coupling agent in aluminum hydroxide [AI(OH),] highly filled linear low-density polyethylene (LLDPE) composite. It is found that AAgPE improves the interfacial adhesion between the filler and the polyethylene matrix, which results in good mechanical properties of the composite. Silicon oil is an effective additive for improving the impact strength, the elongation at break, and the rheological property of the filled composite, but it decreases the tensile strength remarkably. The combination of AAgPF and silicon oil can lead to good performance of the composite. Flammability properties and fracture surface morphologies of the composites through scanning electron microscopy were investigated. The relationship between mechanical properties and microstructure of the composites was discussed.