The work aims to study the effects of multi-walled carbon nanotubes (CNT) of different contents on the mechanical properties of polypropylene/potassium hexatitanate whisker composite. The multi-walled CNT subject to surface modification treatment and the modified potassium hexatitanate whisker, polypropylene (PP) and maleic anhydride grafted polypropylene (PP-g-MAH) were prepared into PP/PP-g-MAH/SPTW/carbon nanotube composite with the two roll mill in the melt-blending method. The effects of modified multi-walled CNT of different contents on the mechanical properties of PP/PP-g-MAH/SPTW composite were compared. The multi-walled CNT surface treated by mixed acid was distributed uniformly in the composite and well bonded with the polymer matrix interface, which toughened and strengthened the composite. However, when the CNT was of larger mass fraction and began to agglomerate, the mechanical properties of the composite would be reduced instead. When the CNT mass fraction is around 0.5%, the composite has the best mechanical properties.