A method for manufacturing an electronic device is disclosed. In the method, a first shell and a second shell are formed. The first shell and the second shell are assembled with each other to form a casing for receiving an electronic module. The two opposite ends of the casing respectively have a first opening and a second opening. The first opening and the second opening are aligned with each other along an extending direction. A seam is located at an outer surface of the casing and between the first shell and the second shell. A paint level is formed on the outer surface of the casing to cover the seam. The casing is moved toward a water transferring film along the extending direction which is vertical to the water transferring film for connecting the water transferring film with the paint level.