Based on the design of molecular structure, a novel high-efficient char-forming agent PECN was synthesized. PECN was combined with silica-gel microencapsulated ammonium polyphosphate (OS-MCAPP) to prepare the intumescent flame retardants (IFR). The results are shown that PP with 30% IFR (m(OS-MCAPP)∶m(PECN)=2∶1) achieves the highest limiting oxygen index (LOI) of 28.8, meanwhile, its peak heat release (pHRR) is 885.5 W/g, which is decreased by 26.2% than that of pure PP. In addition, this PP/IFR composite shows an excellent thermal stability, the residue mass at 700 ℃ is 18.4%, which has a big increase than that of pure PP. Photos of scanning electron microscope show that PECN facilitates the generation of intumescent char layer which present the morphology with high-quality. This char layer protects the matrix and improves the flame retardant.