Abstract: Traditional paper exhibits poor water vapor and oxygen barrier properties due to its high hydroxyl content and porous structure, limiting its applications in many fields, particularly in high-barrier packaging. To enhance the hydrophobicity and gas barrier properties of paper, in this study, TEMPO-oxidized cellulose nanofiber (TOCNF) and cellulose nanocrystal (CNC) were prepared, and hydrophobic stearoylated cellulose nanocrystal (SCNC) was synthesized by esterifying CNC with stearyl chloride. Subsequently, using paper composed of cellulose fibers on the microscale as the substrate, TOCNF was coated onto one side of the paper by vacuum filtration, and SCNC dispersion was uniformly drop-coated onto the other side, ultimately preparing the micro/nano-fiber composite paper. The surface morphologies, water vapor and oxygen barrier properties of the micro/nano-fiber composite paper were characterized. The results show that, compared to the base paper, the micro/nano- fiber composite paper exhibits a significant reduction in oxygen transmission rate to 36.68 cm³·m⁻²·day⁻¹·0.1 MPa⁻¹; the water vapor barrier property is improved, with a water vapor transmission rate decreasing by 16.2% to 500.7 g·m⁻²·day⁻¹. Meanwhile, the water contact angle on the SCNC-deposited surface reaches 112.6°, demonstrating excellent hydrophobicity. This composite paper offers a new approach to expanding paper-based packaging applications, with potential to replace certain petroleum-based packaging materials.