Abstract: Ultrananocrystalline diamond has excellent physical and chemical properties. The ultrananocrystalline diamond films prepared by chemical vapor deposition draw great attention of researchers in recent years. In this paper, properties of ultrananocrystalline diamond and other CVD diamond were compared. The growth mechanism of ultrananocrystalline diamond were described concisely. The basic principles,characteristics and research achievements of the various chemical vapor deposition technique for preparing ultrananocrystalline diamond were explained briefly. Finally, the application of ultrananodiamond and further research were discussed in detail.