Montmorillonite was introduced into the multicomponent epoxy resin by using the intercalation polymerization. Intercalation effect of epoxy/montmorillonite composite system and the influence of the addition of montmorillonite on the glass transition temperature (Tg), mechanical properties and barrier of H2S to coating under high temperature and pressure conditions were investigated. The results showed that it was easy to intercalate epoxy resin into the organic montmorillonite layers, and the interlayer spacing of Montmorillonite was further swelled. In addition, the epoxy/montmorillonite nanocomposite coating with intercalated/ exfoliated structures were prepared. Compared to pure epoxy coating, the heat resistance and mechanical properties of epoxy/montmorillonite nanocomposite coating were slightly improved, and the barrier efficiency to H2S was substantially increased under high temperature and pressure oil-gas environment.