AgCl　and　AgBr　are　a　special　type　of　superionic　conductor,　whose　superionic　phase　transition　does　not　accompany　any　first-order　structural　phase　transition.　In　the　paper,　the　ionic　conductivity　of　AgBr　is　investigated　by　the　first　principles　calculations　with　VASP　code.　The　calculated　results　show　that　the　isolated　charged　interstitial　or　vacancy　is　always　more　stable　than　the　neutral　one　whether　the　system　is　doped　or　not:　the　interstitial　hops　along　＜　001　＞　direction,　and　the　potential　barrier　is　0.29　eV;　the　vacancy　hop　mainly　along　＜　111　＞　direction,　and　the　barrier　is　0.16　eV:　the　migration　barrier　of　vacancy　is　obviously　lower　than　that　of　interstitial,　and　then　the　ionic　conductivity　is　mainly　due　to　the　diffusions　of　vacancies.　Crown　Copyright　(c)　2009　published　by　Elsevier　B.V.　All　rights　reserved.