A method for constructing an external circuit structure is provided. The method is applied to an inner circuit substrate, wherein, the method comprises: laminating a copper foil and a prepreg on the inner circuit substrate; wherein, the prepreg is laminated between the copper foil and the inner circuit substrate; drilling at least one blind via from the copper foil to reach the copper circuit of the inner circuit substrate; removing smear generated in the at least one blind via during the drilling process; corroding off the copper foil; electroless copper plating on the prepreg to form an electroless plating copper layer on the prepreg; wherein, during the electroless copper plating process, a swelling process without desmearing process is implemented.