Abstract: Conventional petroleum-based plastic packaging has caused a global sustainability crisis because of their dependence on non-renewable resources and environmental durability. Chitin, the second most abundant biomass resource in nature after cellulose, can be converted into micro-nanofibers that are lightweight, high strength, biodegradable and biocompatible. Demineralized crab shells were mechanically fibrillated into the micro-nano scale and subsequently surface-modified to prepare partially deacetylated chitin microfibers and carboxylated chitin nanofibers. The microfibers and nanofibers were mixed at a 1∶1 mass ratio to construct a chitin film with a micro-nano fibrous network structure. Calcium-ion cross-linking was then introduced to produce the cross-linked chitin micro-nanofiber (CaMNF) film, whose microstructure, mechanical, optical, water-resistant and thermal properties were systematically characterized. The results demonstrate a significant enhancement in the mechanical properties of the CaMNF film, with a dry tensile strength of 216.7 MPa and a wet tensile strength of 47.1 MPa. Additionally, the film exhibits a light transmittance of 83.6% and a haze of 10.7%. It maintains good structural stability at 250℃ and is fully biodegradable under natural conditions. Owing to these advantageous properties, the CaMNF film shows great potential for applications in flexible substrates, smart labels, biodegradable packaging.