A method that has a step (a) of melt-kneading 0.003 to 0.3 part by mass of an organic peroxide, 0.5 to 400 parts by mass of an inorganic filler, and more than 2 parts by mass and 15.0 parts by mass or less of a silane coupling agent, with respect to 100 parts by mass of a resin containing a halogen-containing resin, at a temperature equal to or higher than a decomposition temperature of the organic peroxide, to prepare a silane master batch; a heat-resistant crosslinked resin formed body obtained by the method, a silane master batch, a mixture and a formed body thereof, and a heat-resistant product.