The work aims to better understand the chemical reactivity between hemicellulose and fibrillated cellulose during processing, and to create an alternative possibility for using bagasse xylan biopolymers in materials and products. With bagasse fiber as raw material, fibril fibers were prepared by mechanical method and then treated by NaOH. The fibrillated fiber suspensions and cellulose films were characterized by fiber length analyzer (FLA), laser particle scattering (LPS), contact angle analyzer (CA), water vapor transmittance analyzer (WVTR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The composition, particle size and electrical charge of treated cellulose suspensions, as well as the morphology, structure and properties of cellulose film were investigated. After the treatment by NaOH with a concentration more than 10%, the content of hemicellulose decreased by about 6%, the crystalline area of cellulose changed, and the stability of fiber suspension greatly decreased. When the hemicellulose content was more than 20%, the cellulose film showed excellent water vapor barrier and hydrophobic properties, with the contact angle of 94°±4°. Both the interaction between hemicellulose and fibrillated fibers of bagasse and the substitution reaction of hemicellulose side groups have significant influence on the composition, structure and properties of cellulose materials.