The invention discloses film covering glue and a preparation method thereof. The preparation method comprises the steps of (1) adding 880-900 weight parts of water in a reaction kettle, mixing, regulating the temperature to 40-50 DEG C, then adding 75-80 weight parts of polyvinyl alcohol, raising the temperature to 40-50 DEG C and holding for 42-48min; (2) regulating the temperature to 80-85 DEG C, adding 135-150 weight parts of formaldehyde, raising the temperature to 90-95 DEG C, holding for 55-65min, regulating a pH value to 4.4-4.6, then adding 450-500 weight parts of melamine modified phenolic resin adhesive, and uniformly mixing; and (3) regulating the pH value to 9.4-9.6 to obtain the film covering glue. The preparation method of the film covering glue is simple to operate and is beneficial to industrial production. The film covering glue prepared by the preparation method has the advantages of high brightness, good surface abrasion resistance, and good flexibility.