The work aims to study the degradation mechanism of widely used PBAT-PLA biodegradable packaging under controlled aerobic compost, so as to provide an important theoretical basis for the large-scale promotion of biodegradable plastics. According to GB/T 19277.1-2011, the biodegradation test (i.e., industrial compost) of PBAT-PLA packaging was carried out for 160 days under the aerobic condition at (58±2) ℃. The biodegradable microcrystalline cellulose was used as reference. The materials before and after degradation were analyzed by infrared ray, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS). The lipase activity of the compost was also tested. The degradation mechanism was explored from multiple angles. The lipase activity of compost containing PBAT-PLA packaging and microcrystalline cellulose was more than 3 times that of blank compost. Infrared spectra showed that the absorption peak formed by water molecule adsorption, sugar ring opening and group oxidation in microcrystalline cellulose was strengthened. The peak of ester bond in PBAT-PLA packaging was significantly weakened. SEM showed that the surface of degraded PBAT-PLA packaging was covered with biofilm. EDS showed that carbon content decreased significantly and oxygen content increased. Microorganisms grow on the surface of PBAT-PLA packaging and form biofilm, and then secrete lipases to hydrolyze the ester bond in PBAT-PLA, so that the polymers are degraded into intermediates or small molecules with different chain lengths, accompanied by oxidation. Finally, the polymers are metabolized and utilized in degradation related microorganisms as a carbon source, forming final metabolites.