Disclosed is a preparation method of an exfoliated nitropolymer/silicate nanocomposite by emulsion polymerization of monomers forming the polymer in an aqueous dispersion of non-modified, layered silicate in the presence of a reactive emulsifier having both a radical-polymerizable vinyl group and a functional group with affinity for silicate. In the process of the polymerization, silicate is fully exfoliated and uniformly dispersed in the polymer. Therefore, only a small amount of silicate is sufficient to improve thermal and mechanical properties of the polymer. Further, the method is advantageous in terms of a simple preparation process due to no use of organo-modified silicate, thus achieving an economic benefit.