The invention discloses a method for preparing a DFN package device with high thermal conductivity, comprising the following steps of: S1, uniformly mixing silicon micro-powders and a flame retardantwith 3-aminopropyltriethoxysilane for surface treatment; S2, adding epoxy resin, linear phenolic resin, liquid nitrile rubber, diethyl pyrocarbonate, polyethylene glycol monooctyl phenyl ether, cellulose acetate butyrate, 5-fluoro-2-meth-oxyaniline, 2,4,6-tris(dimethylaminomethyl)phenol and a release agent, and uniformly mixing the same; and S3, mixing the mixture at 90-110 degrees centigrade for3 to 5 minutes, cooling, pulverizing and sieving a product. The DFN package device with high thermal conductivity prepared by the method has a low incidence rate of internal pores, and avoids electrical property failure due to the deterioration of the thermal conductivity caused by the pores.