Poly(adipate butylene-to-terephthalate)/poly(lactic acid) (PBAT/PLA) blends were prepared by melt blending using aluminate coupling agent (ACA) as compatibilizer. The effects of ACA content on the structure and properties of PBAT/PLA blend system were investigated by FT-IR, melt indexer, differential scanning calorimeter, rotational rheometer, dynamic mechanical thermal analyzer, SEM and servo control tensile testing machine. The results show that ACA interpenetrates between PBAT and PLA molecular chains, causing physical entanglement with PBAT and PLA, increasing intermolecular distance, improving molecular chain compliance, and enhancing the force between PBAT and PBAT. The compatibility of the two phases is improved, and the tensile toughness of PBAT/PLA/ACA blend is increased. The elongation at break of PBAT/PLA/ACA blend is increased from 250.9% to 410.7%. The ACA has a remarkable plasticizing effect, which increases the melt mass flow rate, and the storage modulus, loss modulus, complex viscosity and glass transition temperature of PBAT and PLA of the blend systems are reduced, and the crystallinity of PLA in the blend systems is increased from 18.8% to 26.6%.