Multiwalled carbon nanotubes (MWNTs) are fillers of choice for composite reinforcement owing to their outstanding modulus and strength. However, the poor dispersion and load transfer between MWNTs and matrix still limit their potential and further application of MWNTs in mechanical reinforcement. In this paper, we report a facile one-pot method for functionalization of MWNTs with PPTA-oligomer (o-PPTA). The obtained o-PPTA functionalized multiwalled carbon nanotubes (MWNTs/o-PPTA) can be well dispersed in DMF solvent. Polyvinyl chloride (PVC) was chosen as a model polymer for investigating the reinforcement effect of MWNTs/o-PPTA. The results of tensile tests illustrated that the Young's modulus, toughness and yield strength of composite films were obviously improved compared to those of neat PVC film, which were increased by 129%, 262% and 126%, respectively. The factors including molecular weight of loaded o-PPTA and dosage of MWNTs/o-PPTA on PVC reinforcement effect were also studied. The results showed that MWNTs/o-PPTA is promising additive for reinforcing PVC.