9%(by mass) of MoO3, MoSi2 and Fe2O3 were used to improve the fireproof performance of the ammonium polyphosphate pentaerythrite melamine intumescent coating(APP PER MEL coating) and three coating formulations were established. Four coatings were tested by thermo gravimetric analysis(TGA) and the residual chars of them were tested by infrared(IR) spectrum. The results show that the mass of residual is char increased and it is found that the reason for that is some groups of aromatic structure with better thermal stability promote the form ation of char by MoO3, MoSi2 and Fe2O3.