The purpose of this paper to enhance the packaging performance of poly (butylene adipateco terephthalate) (PBAT) packaging films by blending SAL with PBAT and broaden the application in packaging field. In this paper, alkali lignin was functionalized with tert-butyldimethylsilyl groups by the reaction with tert-butyldimethylsilyl chloride. Then SAL and PBAT were processed into blown films. The mechanical properties and barrier properties of the packaging films were discussed. Compared with the pure PBAT films, the tensile strength of SAL/PBAT composite packaging films increased by 31.0%, the elongation at break decreased by 37.4%, the elastic modulus increased by 529.7%, the oxygen transmittance decreased by 39.4%, and the water vapor transmittance decreased by 42.4%. Therefore, the composite of modified lignin and PBAT can produce synergistic effect, which can effectively improve the mechanical and barrier properties of SAL/PBAT composite packaging films.