Enhancement of the specific heat capacity of a molten salt-based nanofluid is investigated via molecular dynamics (MD) simulations. The results show that the addition of nanoparticles indeed enhances the specific heat capacity of the base fluid. Combining the analysis of potential energy and system configurations, the main reasons responsible for the enhancement of the specific heat capacity of the nanofluid are revealed. Different from previous reports on nanofluids, there is no correlation between the specific heat capacity and the potential energy magnitude of the nanofluid system. It is noticed that the trend of change in the potential energy with nanoparticle loading is only related to the relative magnitude of the nanoparticle and the base fluid potential energy. Moreover, the introduction of nanoparticles introduces an extra force into the system and causes the formation of a compressed layer around the nanoparticle. This structure is tighter than the pure base fluid and requires more energy to be broken. The extra energy used to break this structure can act to enhance the specific heat capacity of the nanofluid. Our research reveals the mechanism behind the specific heat capacity enhancement and guides the prediction of thermal properties and material selection of the nanofluid.