The invention discloses a preparation method of a high temperature resistant QFN package structure. The QFN package structure comprises a heat dissipation pad, a chip and conductive pads which are located in an epoxy insulator, wherein the chip is located on the heat dissipation pad, a plurality of conductive pads are disposed around the heat dissipation pad, and the conductive pads and the chip are connected by a lead. The method comprises the following steps of S1, firstly uniformly mixing the silicon micropowder and the flame retardant with gamma-methacryloxypropyltrimethoxysilane for surface treatment; S2, adding epoxy resin, novolac resin, liquid nitrile rubber, diphenylmethane diisocyanate, diethyl pyrocarbonate, dibenzyl phosphate, 5-fluoro-2-methoxyaniline, 2,4,6-tris(dimethylaminomethyl)phenol and a release agent. The preparation method has excellent heat resistance under the premise of ensuring good mechanical properties, and the glass transition temperature reaches 190-230 DEG C, which can meet the requirements of the packaging of high power and high heating chips.