The flammability properties of an intumescent fire retardant polypropylene added with magnesium hydroxide was discussed in this study. To evaluate the flammability of the material, limit oxygen index, smoke emission, tensile strength, and our exploitation dynamic flammability evaluation system, tests were assessed in experiments. The results showed that the intumescent flame retardant ammonium polyphosphate-filled polypropylene has superior flammability properties but higher carbon oxide (CO) concentration and smoke density. By adding some magnesium hydroxide additives in intumescent fire retarded polypropylene, the smoke density and CO concentration decrease; and the compound also has superior fire properties. It is concluded that intumescent system and magnesium hydroxide additives are effective on improving combustion properties for polypropylene.