A novel type of diamond/Si nano-composite thin films is proposed to improve the performance and quality of nano-diamond films. The function of Si atoms in the formation was explored by analysing the evolution of C and Si atoms in diamond/Si nano-composite films. The adsorption, migration, and evolution of the C-Si island configurations on the diamond (0 0 1) surface was studied by using first-principle method based on the density functional theory (DFT). The results indicate that the maximum adsorption energy of the C and Si atoms on the diamond (0 0 1) surface are 4.96 and 4.39 eV, respectively, which implies Si atoms tend to diffuse out of the diamond crystal and formed C-Si interface on the grain boundary. In the same migration pathway, the migration activation energy of the Si particle was 0.865 eV, and the C particle was 1.957 eV. Therefore, the Si atoms migrated easily onto diamond (0 0 1) surface. In the 3C-1C-1 configuration, the C atoms outside the 3C island migrated into the island to form a 4C island in the diamond structure. However, in the 3C-1C-2 configuration, the C atoms outside the 3C island did not migrate into the 3C island, which destroyed the diamond surface. In the 3C-1Si-1 and 3C-1Si-2 configurations, Si atoms migrated into the 3C island to form the 3C1 Si island. The Si atoms stabilized the structure of the diamond and eliminated non-diamond carbon atoms, hydrogen atoms and defects in the nano-diamond films. (C) 2015 Elsevier B.V. All rights reserved.