A method for bonding fluororesin films, a wide fluororesin film obtained by the method, and a covering material for agricultural use, made thereof, are presented. A method of bonding films (A), wherein two sheets of films (A) made of a fluororesin, are disposed so that their edges overlap each other, a central part (b1) of the overlapping portion (B) is press-bonded under heating at a temperature within a range of from lower by 5° C. to higher by 20° C. than the melting point of the fluororesin, and then the entire area of the portion (B) is press-bonded at a temperature within a range of from lower by 30° C. to lower by more than 5° C., than the melting point, to weld the two sheets of films (A); a wide fluororesin film obtained by the method; and a covering material for agricultural use, made thereof.