A semiconductor package structure and a fabrication method thereof are provided. The fabrication method comprises: providing a substrate strip, the substrate strip comprising a plurality of substrate units; disposing a plurality of chips on the plurality of substrate units; disposing a packaging encapsulant on the substrate strip to encapsulate the chips; forming a warp-resistant layer on a top surface of the packaging encapsulant; and dividing the substrate strip to separate the plurality of substrate units to further fabricate a plurality of semiconductor package structures, wherein the warp-resistant layer is formed of a selected material with a selected thickness to make a variation of warpage of the semiconductor package structure at a temperature between 25° C. and 260° C. to be smaller than 560 μm.