BaZr0.1Ce0.7Y0.2O2.9　(BZCY)　powder　was　synthesized　by　a　homogeneous　coprecipitation　method,　and　the　powder　was　mixed　with　carbonate　to　prepare　the　compound　with　different　ratios　of　(Li/Na)(2)CO3.　The　structure　and　electrical　properties　of　the　composite　electrolytes　were　characterized　by　SEM,　XRD　and　TG-DTA.　The　results　show　that　the　carbonate　in　the　amorphous　form　exists　in　the　composite　electrolytes,　which　reacts　with　BZCY　to　form　BaCO3.　The　conductivities　of　the　composite　electrolytes　reach　0.095　S.cm(-1)　at　600　degrees　C　and　0.071　S.cm(-1)　at　450　degrees　C　in　air,　while　0.126　S.cm(-1)　at　600　degrees　C　and　0.075　S.cm(-1)　at　450　degrees　C　in　humidified　hydrogen.　The　conductivity　of　the　composite　electrolytes　is　basically　stable　for　a　long　time　in　0.08　similar　to　0.09　S.cm(-1)　within　400　h　at　600　degrees　C.　The　single　cell　prepared　with　BZCY-20%　(Li/Na)(2)CO3　composite　electrolytes　shows　good　output　performance.　The　maximum　power　densities　reach　741　mW.cm(-2)　at　600　C-degrees　and　258　mW.cm(-2)　at　500　degrees　C.　When　discharging　with　0.6　A.cm(-2)　at　600　degrees　C,　the　output　performance　is　basically　kept　above　300　mW.cm(-2)　within　90　min.