Radio Frequency Identification (RFID) is a new automatic identification technology. Widespread application of RFID may leak user's privacy. To solve this problem, an improved RFID privacy protection scheme based on Hash-chain is proposed, in which a database identifier field is introduced in RFID tag. When a RFID tag is identified by a reader, by using of the database identifier field, the reader can quickly decide whether the RFID tag belongs to the database system that the reader is associated with. Further treatment is not required if the RFID tag doesn't belong to the database system, thus the privacy of any RFID that isn't relevant with the database is protected. The identification load will be reduced remarkably and the efficiency will be improved evidently in the new authentication scheme.