The morphology of tetrahexahedral nanocrystals could be understood on the basis of a hypothesis that the atoms or molecules on or near spherical surfaces can migrate till reaching their equilibrium positions. Such migration of atoms/molecules is shown to be closely related to the formation of high-index surfaces in nanopolyhedrons.On account of this hypothesis, a theoretical calculation about the indices of the surfaces in tetrahexahedrons is found in good agreement with the empirical results. A group of high-index surfaces for nanocrystals that can be formed under certain environments are thus predicted. This study may provide a novel idea for preparing the catalysts at nanoscale.