We report the structural evolution of two-dimensional (111)-oriented diamond films modulated by the layer number (n) based on first-principles calculations. At n <= 5, the film is relaxed into a few graphene layers; whereas for 6 <= n <= 11, a gradient-graphite-diamond-like (GGDL) structure with gradient changes of interplanar spacing and buckling feature is predicted. A threshold n = 12 is determined to realize the thinnest two-dimensional (111)-oriented diamond film. The analysis of electronic band structures reveals the transition from semimetal to wide band semiconductor with the increase of n. (c) 2012 Elsevier B.V. All rights reserved.