Based on public key, a quantum identity authenticated (QIA) system is proposed without quantum entanglement. The public key acts as the authentication key of a user. Following the idea of the classical public key infrastructure (PKI), a trusted center of authentication (CA) is involved. The user selects a public key randomly and CA generates a private key for the user according to his public key. When it is necessary to perform QIA, the user sends a sequence of single photons encoded with its private key and a message to CA. According to the corresponding secret key kept by CA, CA performs the unitary operations on the single photon sequence. At last, the receiver can judge whether the user is an impersonator. Based on public key, a quantum identity authenticated (QIA) system is proposed without quantum entanglement. The public key acts as the authentication key of a user. Following the idea of ​​the classical public key infrastructure (PKI), a trusted center of authentication ( CA) is involved. The user selects a public key randomly and CA generates a private key for the user according to his public key. When it is necessary to perform QIA, the user sends a sequence of single photons encoded with its private key and a According to the corresponding secret key kept by CA, CA performs the unitary operations on the single photon sequence. At last, the receiver can judge whether the user is an impersonator.