The nature of interface plays a very important role in the properties of nanoparticle-reinforced polymer nanocomposites. Understanding the interfacial interactions is crucial in further development of such nanocomposites. In this work, density functional theory is used to examine the interfacial interactions in the clay-nylon 6 nanocomposites. In particular, comparison has been made the systems in the absence of surfactant and in the presence of surfactant. It is found that surfactant can enhance the interfacial interactions through the formation of hydrogen bonds with clay surface and nylon 6. The interaction energies among the different components are calculated for the systems with clay of different atomic substitution.