Abstract: The way of mimicking the ordered "brick and mortar" structure in natural shells to prepare high-strength functional composite materials with cellulose and inorganic substances of which the interface bonding is the key to achieving ideal structure and performance is a potential excellent choice for producing naturally degradable packaging films. The single interfacial binding force between nanocellulose and montmorillonite results in insufficient mechanical properties. In this work, carboxymethyl cellulose nanofibers (CNFMG) and montmorillonite (MTM) nanosheets were used to prepare pearl layer films in which chitosan (CS) enhanced interface bonding through electrostatic interaction. The effects of electrostatic interactions between CS, CNFMG, and MTM on the structure, mechanical properties, and thermal stability of nanocomposites were studied. The results indicate that MTM in the composite membrane was orderly dispersed in nanosheet form between CNFMG networks. Compared with the CNFMG-MTM binary film, the tensile strength of the ternary film with the addition of CS reached 119.2 MPa, which doubled the strength. The fracture energy reached 10.9 MJ/m³, and the toughness was increased by 5.4 times. The composite film was semitransparent and had good UV shielding properties. The addition of CS also enhanced the thermal stability of the composite film. The research results of this article can provide ideas for the research and application of cellulose based pearl layer biomimetic materials.