National Digital Library long term criterion funded by National Library of China digital resources self-building outsourcing resources of national cultural information sharing project 340TB :off-line/near-line 55TB: on-line Goal: investigate and constitute preservation metadata frames establish the information package criterion and application guideline based on OAIS information model propose the technical application scheme of digital preservation Difficulties and Questions Concept of preservation metadata? Administrative metadata? Contain some of descriptive, structural and administrative metadata? Out of above three? Metadata guideline is established according to format types or resource types? Most appropriate storage medium? CD? Tape? disk? others? 10% CD-ROMs are destroyed. Tapes are difficult to manage. Which technical scheme is suitable? migration, emulation, UVC? Some existing preservation systems? Typical project recommended? PANDORA, NEDLIB, PLANETS, PORTICO, KOPAL etc.