The invention discloses a preparation method of an insert of a hot-stamping forming die. The preparation method comprises the following steps (1) a lower half part shape of a conformal cooling water channel is machined on a common forged steel or cast steel base body, and a copper alloy pipeline corresponding to the conformal cooling water channel in shape is arranged on the lower half part shape;(2) electric-arc additive manufacturing of a transition layer is conducted on the surface of the base body and the surface of the copper alloy pipeline, wherein the transition layer is made from copper alloy; (3) the die insert subjected to electric-arc additive manufacturing is tempered at a high temperature and is then slowly cooled, and the transition layer is machined till the distance between the transition layer and the working surface of the die is 1-2 mm; and (4) a reinforcing layer resistant to high-temperature abrasion is formed on the surface of the machined transition layer through laser cladding, and the reinforcing layer formed by laser cladding is machined till the shape of the working surface of the die and the size precision of the die meet requirements. By adoption of the preparation method, the problem of difficult machining of the conformal cooling water channel is solved, the cooling efficiency is improved, and the die manufacturing cost is reduced.