A　conference-key　protocol　is　used　to　establish　a　common　conference　key　K　such　that　a　group　of　people　can　communicate　securely　over　a　public　network.　To　improve　the　implementation　efficiency　of　Tzeng＇s　conference-key　agreement　protocol,　an　efficient　conference-key　agreement　protocol　is　proposed　under　the　authenticated　broadcast　channel.　First,　the　improved　protocol　is　round-efficient,　and　relaxes　the　waiting　time　for　fault-check.　Second,　it　reduces　the　computational　complexity　by　revoking　the　signature　procedure　in　the　Tzeng＇s　protocol.　It　is　provably　secure　in　the　standard　model　under　the　DDH　assumption.