The synergistic effects of silicotungstic acid (SiW_(12)) as a carelyst in the phosphorus-nitrogen compounds AM-based intumescent flame-retardant (IFR) polypropylene (PP) were studied using the limiting oxygen index(LOI), the UL-94test, thermogravimetric analysis (TGA), real time Fourier transform infrared (FTIR), laser Raman spectroscopy (LRS). TheLOI data show that SiW_(12) added to PP/IFR systems has a synergistic FR effect with an IFR additive named AM. The TGAdata show that SiW_(12) apparently increases the thermal stability of the PP/IFR systems at high temperature (T>500℃). TheFTIR results provide the positive evidence that IFR can improve the thermal stability of PP and SiW_(12) can induce a higherrate of formation of phosphoric acid and its derivatives. The LRS measurements provide useful information on thecarbonaceous microstructures. In short, a suitable amount of SiW_(12) (1.5 wt%) exerts synergistic effects with the IFR byincreasing the LOI value and the thermal stability at high temperature and promoting the formation of charred structures onthe burning PP surface. The synergistic effects of silicotungstic acid (SiW_ (12)) as a carely in the phosphorus-nitrogen compounds AM-based intumescent flame-retardant (IFR) polypropylene (PP) were studied using the limiting oxygen index (LOI) The LOI data show that SiW_ (12) added to PP / IFR systems has a synergistic FR effect with an IFR additive named AM. The LOI data show that SiW_ (12) added to PP / IFR systems has a synergistic FR effect with an IFR additive named AM. TG Adata show that SiW_ (12) apparently increases the thermal stability of the PP / IFR systems at high temperature (T> 500 ° C). The FTIR results provide the positive evidence that IFR can improve the thermal stability of PP and SiW_ (12) can induce In short, a suitable amount of SiW 12 (1.5 wt%) exerts synergistic effects with the IFR by increasing the LOI value and the thermal stabilit y at high temperature and promoting the formation of charred structures on the burning PP surface.