The　composite　electrolytes　Ce0.8Sm0.2O1.9　-BaCe0.8Sm0.2O2.9(SDC-BCS,　molar　ratio　9:1,　7:3,　5:5　and　3:7)　were　synthesized　by　one-step　citric　acid-nitrate　gel　combustion　method.　In　this　work,　the　effect　of　SDC-BCS　composition　on　the　conductivity　and　electrochemical　performance　were　studied.　The　results　indicate　that　grain　size　and　electrical　conductivity　of　SDC-BCS　increase　with　increasing　of　SDC　content　in　SDC-BCS.　Compared　to　electrolyte　SDC,　the　grain-boundary　conductivity　of　composite　electrolytes　is　much　higher.　The　power　density　of　the　single　cell　NiO-SDC-BCS|SDC-BCS|LSCF-SDC-BCS　which　was　prepared　by　composite　electrolytes　with　different　phase　compositions　increases　with　increasing　SDC　content.　When　the　molar　ratio　of　SDC:　BCS　gets　9:1,the　peak　power　density　of　the　single　cell　is　550　mW/cm2　at　temperature　700　℃,　which　is　3　times　higher　than　that　of　NiO-SDC|SDC|LSCF-SDC　single　cell.　©　2017,　Chinese　Ceramic　Society.　All　right　reserved.