Hydrogenated nanocrystalline silicon thin films were deposited with high hydrogen dilution ratio by plasma enhanced chemical vapor deposition technique. The effects of high hydrogen dilution on the surface topography and mechanical properties of the films were studied with atomic force microscopy and TriboIndenter nano indenter. The results indicate that the average grain size in films deposited with high hydrogen dilution is about 3.18 +/- 0.02 nm. The surface roughness and densification of the films decrease with the increase of hydrogen dilution ratio at certain range, resulting in the enhancement of the elastic modulus E and hardness H. Oppositely, the increase of hydrogen dilution can increase the surface roughness induced by the increase of the cavities on the film surfaces, and lead to the decrease of the elastic modulus and hardness correspondingly. In this paper, the detailed analysis and discussion were carried out to investigate the mechanism of the observed phenomena. (C) 2011 Elsevier B.V. All rights reserved.