<p>Nanocellulose is emerging as a biodegradable alternative to synthetic plastics in food packaging, but the preservation mechanisms of nanocellulose composite films have not yet been understood clearly enough. In this study, the preservation mechanism of jute fibers derived cellulose nanofibril (CNF) coatings for banana storage was explored in terms of both chemical composition and particle size. In terms of chemical composition, the CNF coating prepared from raw jute fibers was most suited for use in banana storage, mainly due to its higher antioxidant and UV protection properties. In terms of particle size, the CNF coating homogenized for 5 passes achieved the best performance in preserving the freshness of bananas, mainly owing to its better oxygen barrier properties. The possible preservation mechanism of jute fibers derived CNF composite films for banana storage is related to the formation of a highly dense structure attributed to the strong hydrogen bonding between cellulose molecules and the plugging effect of noncellulosic components, offering excellent antioxidant, UV resistance, and oxygen barrier properties. This paper provides scientific guidance for the design of nanocellulose composite films for food packaging.</p>