This work aimed to study the influence of different addition amounts of six potassium titanate whiskers (SPTW) on the mechanical properties of polypropylene composite. PP/PP-g-MAH/SPTW composite material was prepared by potassium titanate whiskers modified by silane coupling agent KH550, PP and PP-g-MAH with melt blending method. It was found that the mechanical performance of the composite was greatly enhanced when adding appropriate amount of modified SPTW through comparative test. The study showed that the bending strength, tensile strength and impact strength increased with the increasing SPTW content at first and then decreased as it continued to increase. The results indicated that the bending strength was increased by 21.5% with addition of 12% SPTW and that the tensile strength and impact strength were 19.7% and 31.8% respectively higher than before when the content of SPTW reached 8.3%. SPTW modified by silane coupling agent KH550 was added in polypropylene, the polypropylene has the best mechanical properties when SPTW's mass fraction was 12%.