The present invention provides a forming method of a packaging structure. The method comprises the steps of: bonding functional surfaces of a plurality of semiconductor chips to a carrier plate to form a first shielding layer wrapping the non-functional surfaces and the side wall surfaces of the semiconductor chips, wherein the surface of the first shielding layer is in an ellipsoidal shape; forming a second shielding layer on the first shielding layer; forming a plastic package layer on the second shielding layer and the carrier plate between the semiconductor chips; stripping the carrier plate to form a pre-sealing panel, wherein the back surface of the pre-sealing panel exposes the functional surfaces of the semiconductor chips; and forming an external contact structure connected with bonding pads on the back surface of the pre-sealing panel. According to the formed first shielding layer with the ellipsoidal surface, the first shielding layer can uniformly and completely cover the non-functional surfaces and the side wall surfaces of the semiconductor chips, and when the second shielding layer is formed on the ellipsoidal surface of the first shielding layer, the problems of non-uniform thickness and poor edge coverage of the second shielding layer are solved, so that the whole shielding layer formed by the first shielding layer and the formed second shielding layer is complete, and the shielding effect is improved.