The present disclosure discloses a method for dynamic authentication between a reader and a tag, and an implementing device therefor, to solve the technical problem of necessity of dependence of a traditional authentication method on a real-time, online, reliable and secure connection with a background database, as well as lack of ways for highly autonomous authentication of a tag by a reader. In the present disclosure, only a legitimate reader can obtain corresponding tag authentication information from an authentication database and authenticate or update a corresponding tag status; only a legitimate tag can be processed by the legitimate reader; during the authentication, a dynamic updating mechanism is used for a tag ID which ensures forward security; the reader stores tag information using a hash table and thus increases an authentication speed; data synchronization is achieved cleverly by ways of a counting value. The use of a random number guarantees that a different data packet is used for every authentication, thus hiding tag position information effectively and offering excellent security.