Phenyltrimethoxysilane was used as modifier to modify nanocellulose (CNF), which was then coated on the surface of ordinary A4 paper and cured to obtain phenyltrimethoxysilane modified nanocellulose paper-based barrier coating. The hydrophobicity and mechanical property of blank paper, nanocellulose paper-based coating (CNF coating), phenyltrimethoxysilane modified nanocellulose paper-based coating (M-CNF coating) were characterized by video optical contact measuring instrument and electronic tensile machine. The results show that the water contact angle of the M-CNF coating is 120.3°, which is 17.2° higher than that of the blank paper, and has strong hydrophobicity. The tensile strength, elastic modulus and toughness of M-CNF coating are increased by 314.7%, 332.8% and 297.9%, respectively, compared with blank paper, and the coating exhibits better mechanical properties. The barrier performance test of the coating shows that the air permeability of the M-CNF coating is 2837 s/25 cm³, which is 1233 times lower than that of the blank paper; the water vapor transmission rate is 3.586×10³ g/(m²·24 h), which is 50.0% lower than that of the blank paper and the barrier performance is well. In addition, the SEM images of the M-CNF coating show that the tightly bonded three-dimensional network structure fills in remaining paper pores that the CNF coating fails to fill, giving the coating a strong barrier and toughness.