A production method comprising: (a) a step of melt-mixing a base resin containing a chlorinated polyethylene; an organic peroxide, an inorganic filler, and a silane coupling agent, in specific ratios, at a temperature equal to or higher than a decomposition temperature of the organic peroxide, to prepare a silane master batch; (b) a step of mixing the silane master batch obtained in the step (a) with a silanol condensation catalyst, and then forming the resultant mixture; and conducting at least one of the melt-mixing in the step (a) and the mixing in the step (b) is performed in the coexistence of a chloroprene rubber or a polyvinyl chloride; a heat-resistant chlorine-containing crosslinked resin formed body produced by the method, a silane master batch, a mixture and formed body thereof, and a heat-resistant product.