The work aims to investigate the dispersibility of modified multi-walled carbon nanotubes (MWCNTs) in carboxylated nitrile butadiene rubber (XNBR) and dynamic mechanical properties and action mechanism of reinforced rubber substrate. Self-polymerization and physical modification technology of dopamine was adopted to modify the surface of MWCNTs to increase the polar groups to improve the compatibility with XNBR substrate and the polydopamine modified multi-walled carbon nanotubes were prepared. The surface chemical states of the MWCNTs-P were analyzed by FTIR and XPS. The structural evolution of the MWCNTs-P was investigated by TEM. DMA was used to study the reinforcing effects of carbon nanotubes on XNBR substrate. The action mechanism of MWCNTs-P reinforcing the dynamic mechanical properties of XNBR was explored by SEM and TEM images of composite section. By controlling the concentration of dopamine, the thickness of PDA layer on MWCNTs surface gradually increased from 2 nm to 4 nm. The MWCNTs-P fillers could increase the dynamic mechanical properties of composite before and after aging. SEM test showed that the H-MWCNTs-1.0P-2.0wt% composite had shallower holes on the section after aging. The TEM showed that MWCNTs-1.0P fillers had better dispersion in XNBR substrate than MWCNTs fillers. MWCNTs-P fillers are beneficial to reinforcing the dynamic mechanical properties of XNBR matrix due to their better dispersibility in XNBR substrate.