CNF-PPG nanoparticles were prepared by functionalized cellulose nanofibers (CNF) with γ-aminopropyltriethoxysilane (KH550) as a modifier and using polypropylene glycol (PPG) to coat the modified CNF. CNF-PPG were added as fillers to a polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) polymer matrix and PLA/PBAT/CNF-PPG composite films were prepared using the solution casting method. The films were characterized by FTIR, XPS, SEM, DSC and TG, and the effects of the ratio of PLA to PBAT and the addition of CNF-PPG nano-fillers on the mechanical strength, thermal stability and barrier properties of the films were investigated. The results showed that the PLA/PBAT films had higher toughness and thermal stability than the pure PLA films. When m(PLA):m(PBAT)=90:10, the tensile strength of the composite films reached 33.38 MPa and the elongation at break was 39.97% with the addition of 10% (based on the mass of PLA/PBAT, as below) of CNF-PPG nano-fillers. Compared with pure PLA, the final degradation temperature of the composite film was increased from 394 ℃ to 435 ℃; the water vapor and oxygen permeability coefficients were 4.98×10-14 g·cm/cm2·s·Pa and 8.86×10?14 cm3·cm/cm2·s·Pa, which were reduced by 33.6% and 23.5% compared with pure PLA, respectively.