The　Er3+doped　double　perovskite　Ba2CaWO6　crystal　is　a　promising　ratiometric　thermometer　based　on　the　fluorescence　intensity　ratio(FIR)of　transitions　from　2H11/2　and　4S3/2　to　the　lowered　4I15/2　level.However,the　Ca2+vacancy　defect　caused　by　the　charge　difference　between　rare-earth　ions　and　the　substituted　alkaline-earth　ions　gives　rise　to　the　non-radiative　probability　and　limits　the　thermal　sensi-tivity.Here,the　up-conversion　luminescence　and　thermometric　performance　of　Er3+,Yb3+doped　Ba2CaWO6　are　tuned　by　tri-doping　with　alkaline　ions.The　Ca2+vacancy　defect　can　be　eliminated　by　the　introduction　of　Na+,which　occupies　the　Ca2+site　when　it　is　doped　into　Ba2CaWO6　with　Er3+and　Yb3+.On　the　contrary,the　doping　of　Cs+into　Ba2CaWO6　with　Er3+and　Yb3+enhances　the　defect　concentration　because　it　occupies　the　site　of　Ba2+.Thus,the　tri-doping　of　Na+reduces　the　non-radiative　probability　and　enhances　the　quantum　efficiency　of　Er3+,leading　to　the　improvement　of　the　thermometric　sensitivity　of　Ba2CaWO6.As　a　result,we　get　an　excellent　thermometric　Ba2CaWO6:8％Yb3+,3.5％Er3+,6％Na+powder　with　a　luminescence　lifetime　of　515　us　and　maximum　thermal　sensitivity(Sr)of　1.45％/K,which　is　more　than　three　times　higher　than　that　of　the　BCWO∶Er3+powder.