Bi0.5Na0.5TiO3　(BNT)-based　lead-free　materials　are　important　for　piezoelectric　actuator,　and　several　researchers　have　studied　the　effect　of　B-site　complex　ion　doping　on　strain　in　(Bi0.5Na0.5)TiO3-SrTiO3.　In　this　work,　a　paraelectric　perovskite　Sr(Zn1/3Nb2/3)O-3　(SZN)　with　B-site　complex　structure　was　introduced　into　0.80　(Bi0.5Na0.5)TiO3-0.20SrTiO(3)　(BNTST)　to　investigate　the　phase　structure　and　electrical　properties　as　well　as　the　field-induced　strain　behavior.　The　results　showed　that　SZN　substitution　decreases　the　rhombohedrality　90-gamma　and　induces　the　transition　from　dominant　ferroelectric　to　nonergodic　relaxor　by　shifting　its　TF-R　to　lower　temperatures.　Moreover,　the　field-induced　ferroelectric　domains　cannot　remain　stable　at　room　temperature　when　SZN　substitution　is　large　than　1.0　mol%.　These　behaviors　induced　the　transition　between　nonergodic　relaxor　and　ergodic　relaxor,　which　contributed　to　its　large　strain　and　related　properties.　In　this　work,　this　material　gave　the　largest　bipolar　strain　of　0.43%　and　large　normalized　unipolar　strain　of　505　pm/V　at　the　SZN　content　of　2　mol%　under　8　kV/mm,　and　showed　good　temperature　stability　up　to　100　degrees　C.　The　above　encouraging　results　may　be　helpful　for　further　investigation　of　BNTST-based　ternary　systems　in　search　of　a　potential　Pb-free　piezoelectric　material.