In　traditional　identity　authentication　system　the　user　certificate　is　distributed　by　the　certification　center　as　a　user　authentication　credentials,　but　this　certification　system　has　a　lot　of　deficiencies,　it　is　not　safe.　Aiming　at　the　weakness　of　existing　schemes,　we　propose　a　threshold　authentication　scheme　without　trusted　center＇s　participation.　The　certificate　is　issued　by　the　group　members　together.　A　punishment　mechanism　is　presented　and　incorporated　into　the　scheme.　The　program　is　divided　into　five　stages,　and　at　each　stage　of　the　program　we　analyze　its　security　with　game　theory.　The　result　indicates　that　the　scheme　is　a　robust　and　secure.　©　2010　IEEE.