In　order　to　improve　the　calculation　accuracy　of　core　steel　strain,　a　formula　for　the　core　strain　of　buckling-restrained　braces(BRBS)　addressing　the　stiffness　of　BRB-gust　plate　was　proposed　so　as　to　ensure　BRBS　yielded　as　designed.　The　stiffness　of　the　welded　joint　plate　is　firstly　derived,　and　the　core　strain　formula　considering　the　stiffness　of　the　gust　plate　is　subsequently　established　by　using　the　geometric　relationship　between　the　frame　and　BRB.　The　pseudo-static　test　of　the　full-scale　buckling-restrained　brace　frame　and　finite　element　analysis　were　conducted　to　verify　the　accuracy　of　the　formula.　The　results　from　the　formula,　experiments,　and　finite　element　analysis　are　all　in　good　agreement,　and　60%　of　accuracy　improvement　can　be　achieved　when　calculating　the　story　drift　at　the　time　of　BRBS　yielding,　which　demonstrates　that　the　proposed　strain　formula　is　applicable　to　the　optimization　design　for　the　core　steel　of　BRBS.　©　2019,　Editorial　Department　of　Journal　of　Hunan　University.　All　right　reserved.