The invention belongs to the technical field of a composite membrane, and discloses a nano microcrystalline cellulose enhanced polyvinyl alcohol forward osmosis membrane as well as a preparation method and application thereof. The preparation method of the forward osmosis membrane comprises the following steps: (1) dissolving the polyvinyl alcohol in deionized water, heating, stirring to form a uniform and transparent solution, adding additives, and stirring for uniformly dispersing the additives; (2) adding nano microcrystalline cellulose into the solution in the step (1), and uniformly stirring to form a stable membrane casting solution; (3) coating a mold with the membrane casting solution in the step (2), drying under the room temperature, and volatizing moisture to form a membrane; and (4) immersing the membrane formed in the step (3) into a glutaraldehyde solution, adding an additive into the solution to be subjected to cross-linking reaction, taking out the membrane, and drying the membrane to obtain the nano microcrystalline cellulose enhanced polyvinyl alcohol forward osmosis membrane. The forward osmosis membrane is high in strength, a supporting layer is not needed, the concentration polarization phenomenon in the application process of the positive osmosis membrane can be obviously reduced, and the water flux and the salt interception rate of the membrane can be increased.