Abstract: Linear low density polyethylene (LLDPE) was modified by ternary intumescent flame retardant (IFR) system with organic montmorillonite (OMMT) and nickel carbonate (NC). The thermal behavior and flammability of the composites were evaluated by thermogravimetric analysis (TGA)，limiting oxygen index (LOI) , UL-94 burning test and cone calorimeter (CONE) test. The morphological structure of the composites after combustion was analyzed by Fourier infrared (FT-IR) analysis, digital camera and scanning electron microscope (SEM). Results showed that LOI of LLDPE-IFR-OMMT was 31.5% and the composites could pass UL-94-V-0 rating when mLLDPE/mIFR was fixed at 7/3 and mOMMT/m(LLDPE+IFR) was 0.04. Char residue of the composites was 15.09%, and peak heat release rate (PHRR) of the composites reduced by 50% compared with pure LLDPE. Adding NC to LLDPE-IFR-OMMT composites, the flame retardant properties of the composite significantly increased. When mNC/m(LLDPE+IFR) was 0.02, LOI of LLDPE-IFR-OMMTNC composites reached 32.7%, and char residue of the composites was 19.04%, and PHRR of the composites reduced by 57% compared with pure LLDPE. OMMT and NC could catalyze LLDPEIFR into char. A compact and dense intumescent char was formed after combustion, thus NC and OMMT could enhance the flame retardancy of the composites.