A　quantum　protocol　for　(t,n)-threshold　identity　authentication　based　on　Greenberger-Horne-Zeilinger　states　is　presented.　A　trusted　third　party　(TTP)　can　authenticate　the　users　simultaneously　when　and　only　when　t　or　more　users　among　n　apply　for　authentication.　Compared　with　the　previous　multiparty　simultaneous　quantum　identity　authentication　(MSQIA)　protocols,　the　proposed　scheme　is　more　flexible　and　suitable　for　practical　applications.