The phosphoric acid-pentaerythritol-melamine copolymer, which is composed of three main components of intumescent flame retardant (IFR) and has optimal intumescent degree, was selected as IFR. The influence of meleated polypropylene (PP-g-MAH) on the properties and compatibility of IFR polypropylene (PP) composites were studied. The results obtained from mechanical tests, rheological behavior of composites, and scanning electron microscope showed that PP-g-MAH was a true coupling agent for IFR/PP blends and did not change the necessary flame retardancy. The cocrystallization between bulk PP and PP segments of PP-g-MAH was also proven by WAXD analysis. Flow test showed that the flow behaviors of composites in the melt are those of a pseudoplastic and it is very small for PP-g-MAH affecting rheological behavior of the PP/IFR composite.