A method for manufacturing a composite layer circuit structure of an electronic device is provided. First, a first conductive layer is formed on a carrier plate. Next, a first photoresist layer is formed on the first conductive layer. The first photoresist layer includes multiple first openings exposing part of the first conductive layer. Next, a first electroplating layer is formed in the first openings. Then, the first photoresist layer is removed. Then, a first insulating layer is formed on the first conductive layer. The first insulating layer includes multiple second openings exposing part of the first electroplating layer. In the above, at least one heat treatment process is performed on the first electroplating layer before the first insulating layer is formed on the first conductive layer. A temperature when performing at least one heat treatment process is higher than or equal to 40° C. and lower than or equal to 300° C.