The work aims to enhance the modification effect of CNF and improve the moisture permeability of the prepared PLA/CNF coated paper. AlCl3/ZnCl2 solution system was used to dissolve CNF, and then Y-methacryloyloxypropyltrimethoxysilane (KH-570) modification was performed to obtain dissolution-modified CNF (DMCNF), which was co-mingled with PLA in methylene chloride to obtain the PLA/DMCNF solution. Next, the paper was coated by multifunctional coating experimental machine to obtain the PLA/DMCNF coated paper and the chemical structure and crystal structure of CNF as well as the properties of the coated paper before and after modification were tested. From the XRD and SEM diagrams, it was seen that the crystal shape of CNF was changed and the morphology of fibers was destroyed after dissolution, and the Si content on the surface of DMCNF was 2.64 times higher than that of MCNF as obtained from the XPS diagrams, which directly indicated that dissolution played an obvious role in promoting the modification of CNF. The tensile strength and tensile stress of the coated paper were significantly improved, in which the tensile strength reached a maximum of 39.11 MPa at a coating amount of 10.20 g/m2, which was 83.5% higher than that of the original paper. At a coating amount of 14.85 g/m2, the tensile strain of the coated paper reached a maximum of 6.36%, with a water contact angle of 120.9°, and a water vapor transmission rate of 210.191 1 g/(m2.24 h). Therefore, AlCl3/ZnCl2 dissolution has an obvious promotion effect on CNF modification, and the PLA/DMCNF coating improves the moisture permeability, hydrophobicity and tensile properties of the paper.