In order to improve the quality of nano-diamond films, a new type of diamond/Si nano-composite films was proposed. The monolayer Si interface and monolayer SiC interface were studied in this paper. The system total energies and adsorption energies of monolayer Si and monolayer SiC on diamond (001) surface were calculated with first principle method based on the density functional theory (DFT) to investigate the stability of the two kinds of interface structures in the Diamond/Si nano-composite films. Moreover, the variation of the configuration energy and structures when the hydrogen atom and CH2 radical adsorbed on the two kinds of interfaces were researched to verify whether the diamond phase was able to nucleate and grow or not in the process of diamond/Si nano-composite films deposition. It turned out that (1) the diamond surface structure which is terminated by monolayer silicon atoms is not very stable. It is difficult to form the stable monolayer Si interface in diamond/Si nano-composite films; (2) the monolayer SiC interface with the carbon and silicon atomic ratio of 1:1in which the carbon and silicon atoms are located in the same row respectively is a more stable structure. The interface is conductive to the second nucleation in the process of diamond growth. (C) 2014 Elsevier B.V. All rights reserved.