Abstract:Ultra-density optical storage is introduced from two aspects. One is three-dimension op tical storage including holographic optical storage, two-photon absorp tion storage and multi-layer storage. Holographic storage can record a great deal of data with ultra2density, high speed of addressing and a long life of storage. Two-photon absorp tion belongs to multi-layer storage,which presents various aspects, one of them———photochromatic storage is introduced. Another aspect of ultra-density storage is near-field op tical storage. Contrasting with the conventional far-field optical storage, the most distinctive difference is using optical probe, which is not bigger than some nanometers and the distance from storage medium is less than a few nanometers, to get a storage unit smaller than several nanometers. In the end this ar-ticle also exp resses the development and app lications of ultra2density optical storage.