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.