The invention discloses a nano cellulose reinforced fiberglass composite film and a preparation method thereof. The preparation method comprises the following steps: treating fiberglass, formed through wire drawing, by a soaking agent, and carrying out stirring treatment, thus obtaining a fiberglass suspension solution; then taking and preparing a certain amount of nano cellulose into a nano cellulose suspension solution; adding the fiberglass suspension solution into a flask in which the nano cellulose suspension solution is contained, putting the flask in an ultrasonic oscillator, carrying out acute mechanical stirring, and uniformly stirring and mixing, thus obtaining a required nano cellulose/fiberglass mixed solution; pouring the mixed solution into a polystyrene culture vessel, and evaporating moisture under a room temperature condition; drying for 48 hours in a thermostat, thus obtaining a required fiberglass/nano cellulose composite film. The preparation method disclosed by the invention has the advantages of simple operation, no thermal treatment process and convenient production, and the prepared fiberglass/nano cellulose composite film is high in acid-base resistance and strength and good in antifungal, flame-retardant and heat-resistant properties, and has a better sound insulation effect.