Molecular dynamics simulations have been performed to investigate the coalescence of two spreading droplets on different nano carbon substrates. Simulation results show that the drop formation behavior is influenced by the surface structures of carbon substrates and geometrical shapes of drops. In the case of pillared graphene substrates, the unexpected detachment of Au drops is observed due to the dewettability. Moreover, the increase of minimum height of the bridge connecting drops exhibits power-law behavior, revealing that the bridge evolves with self-similar dynamics, which is further illustrated by the scaling profiles. Our results provide an available method to tune the coalescence of metallic liquid drops with alteration of surfaces or initial shapes, which has important implications in the industrial application such as ink-jet printing and metallurgy.