The cellulose nanocrystals (CNC) was extracted from the shell of Camellia oleifera Abel by chemical disintegration method. The butyrated cellulose nanocrystals (BCNC) was prepared by surface modified with Butyric anhydride, and the BCNC/PLA nanocomposites were prepared by solvent casting method. Morphologies and properties of BCNC were observed, and the tensile properties, barrier properties and the transparency of BCNC/PLA nanocomposites film were studied in this paper. The strength and toughness of PLA were improved by composited with BCNC, and the tensile strength of PLA composites film was improved 30.1% by adding 5 wt% BCNC. Adding 5 wt% BCNC, the water vapor gas permeability and oxygen permeability of the film were decreased by 60.0% and 35.0%, and the composite films still maintain high transmittance. Owing to the excellent dispersion and interfacial adhesion in the matrix, the BCNC have a great influence on the tensile properties and barrier properties of PLA than CNC.