Sites　engineering　has　been　extensively　investigated　in　BaTiO3-based　lead-free　materials.　Although　the　effect　of　A　or　B　site　substitution　on　structure　and　electric　properties　have　been　researched　adequately,　the　synergic　and　competitive　impacts　of　doping　element　have　received　little　attention,　which　has　become　an　urgent　issue　for　further　optimizing　performance.　Here,　three　groups　BT-based　ceramics　[0.6(Ba0.9Ca0.1)TiO3-0.4Ba(Sn0.2Ti0.8)O3,　B(Ca)TS,　0.6(Ba0.9Ca0.05Sr0.05)TiO3-0.4Ba(Sn0.2Ti0.8)O3,　B(Ca,Sr)TS,　and　0.6(Ba0.9Sr0.1)TiO3-0.4Ba(Sn0.2Ti0.8)O3,　B(Sr)TS]　are　synthesized　by　normal　sintering,　revealing　the　synergic　and　competitive　mechanism　of　A　site　doping　on　structure　and　properties.　The　effect　of　Ca2+　and　Sr2+　are　quite　different　on　the　structure,　especially　the　phase　structure　and　grain　size,　and　the　evolution　of　electric　properties　(e.g.,　d33,　Strain,　and　Temperature　stability)　results　from　structure　caused　by　the　synergic　and　competitive　effect　of　Ca2+　and　Sr2+.　For　example,　a　large　d33　(∼950　pC/N)　is　obtained　in　B(Sr)TS　due　to　its　closer　R-O-T　phase　structure　compared　to　B(Ca)TS　and　B(Ca,Sr)TS　ceramics,　which　is　superior　to　some　previous　BT-based　studies.　Therefore,　exploring　of　doping　mechanism　can　further　tune　the　microscopic　structure　and　thus　enhance　electric　properties,　accelerating　the　practical　process　of　lead-free　ceramics.　©　2022　Elsevier　B.V.