A novel triazine charring agent poly(4,6-dichloro-N-butyl-1,3,5-triazin-2-amine-ethylenediamine) (CNCD-DA) was synthesized, which had good thermal stability and char-forming ability. The synergistic effects between ammonium polyphosphate (APP) and CNCD-DA on flame retardant properties and mechanism of polypropylene (PP) were investigated by the limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CCT), scanning electron microscopy (SEM), laser Raman spectroscopy analysis (LRS), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results illustrated when the mass ratio of APP to CNCD-DA was 3:1 with 30% loading, the intumescent flame retardant (IFR) showed the best synergistic effect with LOI value reaching 36.5%, and the IFR could greatly suppress the generation of the flame and smoke during combustion. The results from SEM, TGA, LRS and FTIR indicated that during the combustion IFR could form a continuous and intumescent char containing P-O-P and P-O-C crosslinking structures and polyaromatic structures, thus effectively retard the combustion of PP. (C) 2016 Published by Elsevier B.V.