Objective To study the effect of different methane concentrations on the growth of nanocrystalline diamond films, and to realize the preparation of NCD thin films with smaller grain size and Gaoping integer. Method Nanocrystalline diamond thin films were prepared by microwave plasma enhanced chemical vapor deposition method. The effects of different concentrations of methane on the grain size, surface morphology and surface roughness of nanocrystalline diamond films were discussed with CH4 and H2 as the gas source and other conditions. The surface morphology and grain size of nanocrystalline diamond films were observed by SEM and XRD, and the scattering peaks were analyzed by Raman. Results With the increase of methane concentration, the grain size of the films is decreased, in low methane concentration,