The work aims to prepare polyethylene glycol (PEG200)-acetylated cellulose nanocrystals/ montmorillonite/poly-3-hydroxybutylate-co-3-hydroxycaproate (PHBH) nanocomposite packaging films, and to investigate the effects of PEG200 on the properties of ternary nanocomposite materials (ACNs/MMT/PHBH), in order to increase the dispersion of nanoparticles, improve the flexibility of ternary nanocomposite packaging film, and obtain nanocomposite packaging films with excellent properties, such as flexibility and dispersibility. Different proportions of PEG200-ACNs/MMT/PHBH nanocomposite packaging films were prepared via solution blending method. The section morphology, thermal stability, crystal morphology, mechanical properties, and blocking performance of nanocomposite films were studied through SEM, FTIR, polarizing microscope (POM), TGA, DSC, tensile tester, and Oxygen Permeability and Water Vapor Permeability Detection. The results of SEM show that PEG200 coating on the nanoparticles further improved the compatibility between the packing and PHBH matrix. The results of the mechanical test show that, after PEG200 is added, the toughness of composite packaging film increases to a certain extent. Compared with the packaging film without PEG200 added, the elongation at break of nanocomposite packaging films with 6% PEG200 increases by 29.9%. The barrier performance of the composite film with 4% PEG200 was the best, and the permeability of water vapor and oxygen were 26.48 g/(m2.d) and 28.46 cm3/(m2.d) respectively. The experimental results show that adding a small amount of PEG200 can improve the compatibility between the nanoparticles and PHBH, and improve the toughness and oxygen and moisture resistance of ACNs/MMT/PHBH nanocomposites.