Abstract: The polylactic acid (PLA) has great potential in the preparation of environmentally friendly dielectric materials due to its biodegradability and high strength, but low dielectric constant limits its wide application in this field. The carboxylic multi-walled carbon nanotubes (MWCNTs—COOH), epoxy-based chain extender (ADR) and poly(butylene adipate-co-terephthalate) (PBAT) were introduced into PLA by melt blending to prepare MWCNTs—COOH-ADR-PBAT/PLA composites. The effects of MWCNTs—COOH on the inter-molecular chain interactions, processing, crystallization, dynamic mechanical, mechanical and dielectric properties of the PBAT/PLA reactive compatibilization system were studied by FTIR, Torque rheometer, DSC, DMA, electron universal testing machine, SEM and LCR dielectric measuring instrument, etc. The results show that the carboxyl group in MWCNTs—COOH preferentially reacts with the reactive compatibilizer during the blending process, which reduces the catalytic compatibilization efficiency of the reactive compatibilizer on the interface between PLA and PBAT. At the same time, MWCNTs—COOH preferentially disperse at the two-phase interface under the drive of dynamics and thermodynamics, giving the material a better rigid toughness balance, while significantly improving the dielectric properties of the material. When the MWCNTs—COOH content is 4wt%, the dielectric constant and dielectric loss of MWCNTs—COOH-ADR-PBAT/PLA composite at 100 Hz were 5.35 and 0.06 respectively, and the material had good comprehensive properties.